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These Roman Emperors were infamous for their debauchery and cruelty.
- Roman Emperors were known for their excesses and violent behavior.
- From Caligula to Elagabalus, the emperors exercised total power in the service of their often-strange desires.
- Most of these emperors met violent ends themselves.
We rightfully complain about many of our politicians and leaders today, but historically speaking, humanity has seen much worse. Arguably no set of rulers has been as debauched, ingenious in their cruelty, and prone to excess as the Roman Emperors.
While this list is certainly not exhaustive, here are seven Roman rulers who were perhaps the worst of the worst in what was one of the largest empires that ever existed, lasting for over a thousand years.
Officially known as Gaius (Gaius Caesar Augustus Germanicus), Caligula was the third Roman Emperor, ruling from 37 to 41 AD. He acquired the nickname "Caligula" (meaning "little [soldier's] boot") from his father's soldiers during a campaign.
While recognized for some positive measures in the early days of his rule, he became famous throughout the ages as an absolutely insane emperor, who killed anyone when it pleased him, spent exorbitantly, was obsessed with perverse sex, and proclaimed himself to be a living god.
Caligula gives his horse Incitatus a drink during a banquet. Credit: An engraving by Persichini from a drawing by Pinelli, from "The History of the Roman Emperors" from Augustus to Constantine, by Jean Baptiste Louis Crevier. 1836.
Among his litany of misdeeds, according to the accounts of Caligula's contemporaries Philo of Alexandria and Seneca the Younger, he slept with whomever he wanted, brazenly taking other men's wives (even on their wedding nights) and publicly talking about it.
He also had an insatiable blood thirst, killing for mere amusement. Once, as reports historian Suetonius, when the bridge across the sea at Puteoli was being blessed, he had a number of spectators who were there to inspect it thrown off into the water. When some tried to cling to the ships' rudders, Caligula had them dislodged with hooks and oars so they would drown. On another occasion, he got so bored that he had his guards throw a whole section of the audience into the arena during the intermission so they would be eaten by wild beasts. He also allegedly executed two consuls who forgot his birthday.
Suetonius relayed further atrocities of the mad emperor's character, writing that Caligula "frequently had trials by torture held in his presence while he was eating or otherwise enjoying himself; and kept an expert headsman in readiness to decapitate the prisoners brought in from gaol." One particular form of torture associated with Caligula involved having people sawed in half.
He caused mass starvation and purposefully wasted money and resources, like making his troops stage fake battles just for theater. If that wasn't enough, he turned his palace into a brothel and was accused of incest with his sisters, Agrippina the Younger, Drusilla, and Livilla, whom he also prostituted to other men. Perhaps most famously, he was planning to appoint his favorite horse Incitatus a consul and went as far as making the horse into a priest.
In early 41 AD, Caligula was assassinated by a conspiracy of Praetorian Guard officers, senators, and other members of the court.
Fully named Nero Claudius Caesar, Nero ruled from 54 to 68 AD and was arguably an even worse madman than his uncle Caligula. He had his step-brother Britannicus killed, his wife Octavia executed, and his mother Agrippina stabbed and murdered. He personally kicked to death his lover Poppeaea while she was pregnant with his child — a horrific action the Roman historian Tacitus depicted as "a casual outburst of rage."
He spent exorbitantly and built a 100-foot-tall bronze statue of himself called the Colossus Neronis.
He is also remembered for being strangely obsessed with music. He sang and played the lyre, although it's not likely he really fiddled as Rome burned in what is a popular myth about this crazed tyrant. As misplaced retribution for the fire which burned down a sizable portion of Rome in the year 64, he executed scores of early Christians, some of them outfitted in animal skins and brutalized by dogs, with others burned at the stake.
He died by suicide.
Roman Emperor Nero in the burning ruins of Rome. July 64 AD.Credit: From an original painting by S.J. Ferris. (Photo by Kean Collection / Getty Images)
Like some of his counterparts, Commodus (a.k.a. Lucius Aelius Aurelius Commodus) thought he was a god — in his case, a reincarnation of the Greek demigod Hercules. Ruling from 176 to 192 AD, he was also known for his debauched ways and strange stunts that seemed designed to affirm his divine status. Numerous statues around the empire showed him as Hercules, a warrior who fought both men and beasts. He fought hundreds of exotic animals in an arena like a gladiator, confusing and terrifying his subjects. Once, he killed 100 lions in a single day.
Emperor Commodus (Joaquin Phoenix) questions the loyalty of his sister Lucilla (Connie Nielsen) In Dreamworks Pictures' and Universal Pictures' Oscar-winning drama "Gladiator," directed by Ridley Scott.Credit: Photo By Getty Images
The burning desire to kill living creatures as a gladiator for the New Year's Day celebrations in 193 AD brought about his demise. After Commodus shot hundreds of animals with arrows and javelins every morning as part of the Plebeian Games leading up to New Year's, his fitness coach (aptly named Narcissus), choked the emperor to death in his bath.
Officially named Marcus Aurelius Antoninus II, Elagabalus's nickname comes from his priesthood in the cult of the Syrian god Elagabal. Ruling as emperor from 218 to 222 AD, he was so devoted to the cult, which he tried to spread in Rome, that he had himself circumcised to prove his dedication. He further offended the religious sensitivities of his compatriots by essentially replacing the main Roman god Jupiter with Elagabal as the chief deity. In another nod to his convictions, he installed on Palatine Hill a cone-like fetish made of black stone as a symbol of the Syrian sun god Sol Invictus Elagabalus.
His sexual proclivities were also not well received at the time. He was likely transgender (wearing makeup and wigs), had five marriages, and was quite open about his male lovers. According to the Roman historian (and the emperor's contemporary) Cassius Dio, Elagabalus prostituted himself in brothels and taverns and was one of the first historical figures on record to be looking for sex reassignment surgery.
He was eventually murdered in 222 in an assassination plot engineered by his own grandmother Julia Maesa.
Emperor for just eight months, from April 19th to December 20th of the year 69 AD, Vitellius made some key administrative contributions to the empire but is ultimately remembered as a cruel glutton. He was described by Suetonius as overly fond of eating and drinking, to the point where he would eat at banquets four times a day while sending out the Roman navy to get him rare foods. He also had little social grace, inviting himself over to the houses of different noblemen to eat at their banquets, too.
Vitellius dragged through the streets of Rome.Credit: Georges Rochegrosse. 1883.
He was also quite vicious and reportedly either had his own mother starved to death or approved a poison with which she committed suicide.
Vitellius was ultimately murdered in brutal fashion by supporters of the rival emperor Vespasian, who dragged him through Rome's streets, then likely beheaded him and threw his body into the Tiber river. "Yet I was once your emperor," were supposedly his last words, wrote historian Cassius Dio.
Marcus Aurelius Antoninus I ruled Rome from 211 to 217 AD on his own (while previously co-ruling with his father Septimius Severus from 198). "Caracalla"' was his nickname, referencing a hooded coat from Gaul that he brought into Roman fashion.
He started off his rise to individual power by murdering his younger brother Geta, who was named co-heir by their father. Caracalla's bloodthirsty tyranny didn't stop there. He wiped out Geta's supporters and was known to execute any opponents to his or Roman rule. For instance, he slaughtered up to 20,000 citizens of Alexandria after a local theatrical satire dared to mock him.
Geta Dying in His Mother's Arms.Credit: Jacques Pajou (1766-1828)
One of the positive outcomes of his rule was the Edict of Caracalla, which gave Roman citizenship to all free men in the empire. He was also known for building gigantic baths.
Like others on this list, Caracalla met a brutal end, being assassinated by army officers, including the Praetorian prefect Opellius Macrinus, who installed himself as the next emperor.
As the second emperor, Tiberius (ruling from 42 BC to 16 AD) is known for a number of accomplishments, especially his military exploits. He was one of the Roman Empire's most successful generals, conquering Pannonia, Dalmatia, Raetia, and parts of Germania.
He was also remembered by his contemporaries as a rather sullen, perverse, and angry man. In the chapter on his life from The Lives of the Twelve Caesars by the historian Suetonius, Tiberius is said to have been disliked from an early age for his personality by even his family. Suetonius wrote that his mother Antonia often called him "an abortion of a man, that had been only begun, but never finished, by nature."
"Orgy of the Times of Tiberius on Capri".Painting by Henryk Siemiradzki. 1881.
Suetonius also paints a damning picture of Tiberius after he retreated from public life to the island of Capri. His years on the island would put Jeffrey Epstein to shame. A horrendous pedophile, Tiberius had a reputation for "depravities that one can hardly bear to tell or be told, let alone believe," Suetonius wrote, describing how "in Capri's woods and groves he arranged a number of nooks of venery where boys and girls got up as Pans and nymphs solicited outside bowers and grottoes: people openly called this 'the old goat's garden,' punning on the island's name."
There's much, much more — far too salacious and, frankly, disgusting to repeat here. For the intrepid or morbidly curious reader, here's a link for more information.
After he died, Tiberius was fittingly succeeded in emperorship by his grandnephew and adopted grandson Caligula.
As bad as this sounds, a new essay suggests that we live in a surprisingly egalitarian age.
- A new essay depicts 700 years of economic inequality in Europe.
- The only stretch of time more egalitarian than today was the period between 1350 to approximately the year 1700.
- Data suggest that, without intervention, inequality does not decrease on its own.
Economic inequality is a constant topic. No matter the cycle — boom or bust — somebody is making a lot of money, and the question of fairness is never far behind.
A recently published essay in the Journal of Economic Literature by Professor Guido Alfani adds an intriguing perspective to the discussion by showing the evolution of income inequality in Europe over the last several hundred years. As it turns out, we currently live in a comparatively egalitarian epoch.
Seven centuries of economic history
Figure 8 from Guido Alfani, Journal of Economic Literature, 2021.
This graph shows the amount of wealth controlled by the top ten percent in certain parts of Europe over the last seven hundred years. Archival documentation similar to — and often of a similar quality as — modern economic data allows researchers to get a glimpse of what economic conditions were like centuries ago. Sources like property tax records and documents listing the rental value of homes can be used to determine how much a person's estate was worth. (While these methods leave out those without property, the data is not particularly distorted.)
The first part of the line, shown in black, represents work by Prof. Alfani and represents the average inequality level of the Sabaudian State in Northern Italy, The Florentine State, The Kingdom of Naples, and the Republic of Venice. The latter part, in gray, is based on the work of French economist Thomas Piketty and represents an average of inequality in France, the United Kingdom, and Sweden during that time period.
Despite the shift in location, the level of inequality and rate of increase are very similar between the two data sets.
Apocalyptic events cause decreases in inequality
Note that there are two substantial declines in inequality. Both are tied to truly apocalyptic events. The first is the Black Death, the common name for the bubonic plague pandemic in the 14th century, which killed off anywhere between 30 and 50 percent of Europe. The second, at the dawn of the 20th century, was the result of World War I and the many major events in its aftermath.
The 20th century as a whole was a time of tremendous economic change, and the periods not featuring major wars are notable for having large experiments in distributive economic policies, particularly in the countries Piketty considers.
The slight stall in the rise of inequality during the 17th century is the result of the Thirty Years' War, a terrible religious conflict that ravaged Europe and left eight million people dead, and of major plagues that affected South Europe. However, the recurrent outbreaks of the plague after the Black Death no longer had much effect on inequality. This was due to a number of factors, not the least of which was the adaptation of European institutions to handle pandemics without causing such a shift in wealth.
In 2010, the last year covered by the essay, inequality levels were similar to those of 1340, with 66 percent of the wealth of society being held by the top ten percent. Also, inequality levels were continuing to rise, and the trends have not ended since. As Prof. Alfani explained in an email to BigThink:
"During the decade preceding the Covid pandemic, economic inequality has shown a slow tendency towards further inequality growth. The Great Recession that began in 2008 possibly contributed to slow down inequality growth, especially in Europe, but it did not stop it. However, the expectation is that Covid-19 will tend to increase inequality and poverty. This, because it tends to create a relatively greater economic damage to those having unstable occupations, or who need physical strength to work (think of the effects of the so-called "long-Covid," which can prove physically invalidating for a long time). Additionally, and thankfully, Covid is not lethal enough to force major leveling dynamics upon society."
Can only disasters change inequality?
That is the subject of some debate. While inequality can occur in any economy, even one that doesn't grow all that much, some things appear to make it more likely to rise or fall.
Thomas Piketty suggested that the cause of changes in inequality levels is the difference in the rate of return on capital and the overall growth rate of the economy. Since the return on capital is typically higher than the overall growth rate, this means that those who have capital to invest tend to get richer faster than everybody else.
While this does explain a great deal of the graph after 1800, his model fails to explain why inequality fell after the Black Death. Indeed, since the plague destroyed human capital and left material goods alone, we would expect the ratio of wealth over income to increase and for inequality to rise. His model can provide explanations for the decline in inequality in the decades after the pandemic, however- it is possible that the abundance of capital could have lowered returns over a longer time span.
The catastrophe theory put forth by Walter Scheidel suggests that the only force strong enough to wrest economic power from those who have it is a world-shattering event like the Black Death, the fall of the Roman Empire, or World War I. While each event changed the world in a different way, they all had a tremendous leveling effect on society.
But not even this explains everything in the above graph. Pandemics subsequent to the Black Death had little effect on inequality, and inequality continued to fall for decades after World War II ended. Prof. Alfani suggests that we remember the importance of human agency through institutional change. He attributes much of the post-WWII decline in inequality to "the redistributive policies and the development of the welfare states from the 1950s to the early 1970s."
What does this mean for us now?
As Professor Alfani put it in his email:
"[H]istory does not necessarily teach us whether we should consider the current trend toward growth in economic inequality as an undesirable outcome or a problem per se (although I personally believe that there is some ground to argue for that). Nor does it teach us that high inequality is destiny. What it does teach us, is that if we do not act, we have no reason whatsoever to expect that inequality will, one day, decline on its own. History also offers abundant evidence that past trends in inequality have been deeply influenced by our collective decisions, as they shaped the institutional framework across time. So, it is really up to us to decide whether we want to live in a more, or a less unequal society."
What's the difference between brainwashing and rehabilitation?
- The book and movie, A Clockwork Orange, powerfully asks us to consider the murky lines between rehabilitation, brainwashing, and dehumanization.
- There are a variety of ways, from hormonal treatment to surgical lobotomies, to force a person to be more law abiding, calm, or moral.
- Is a world with less free will but also with less suffering one in which we would want to live?
Alex is a criminal. A violent and sadistic criminal. So, we decide to do something about it. We're going to "rehabilitate" him.
Using a new and exciting "Ludovico" technique, we'll change his brain chemistry to make him an upstanding, moral citizen. Alex will be forced to watch violent movies as his body is pumped with nausea-inducing drugs. After a while, he'll come to associate violence with this horrible sickness. And, after a course of Ludovico, Alex can happily return to society, never again doing an immoral or illegal act. He'll no longer be a danger to himself or anyone else.
This is the story of A Clockwork Orange by Anthony Burgess, and it raises important questions about the nature of moral decisions, free will, and the limits of rehabilitation.
Today's Clockwork Orange
This might seem like unbelievable science fiction, but it might be truer — and nearer — than we think. In 2010, Dr. Molly Crockett did a series of experiments on moral decision-making and serotonin levels. Her results showed that people with more serotonin were less aggressive or confrontational and much more easy-going and forgiving. When we're full of serotonin, we let insults pass, are more empathetic, and are less willing to do harm.
As Fydor Dostoyevsky wrote in The Brothers Karamazov, if the "entrance fee" for having free will is the horrendous suffering we see all around us, then "I hasten to return my ticket."
The idea that biology affects moral decisions is obvious. Most of us are more likely to be short-tempered and spiteful if we're tired or hungry, for instance. Conversely, we have the patience of a saint if we just have received some good news, had half a bottle of wine, or had sex.
If our decision-making can be manipulated or determined by our biology, should we not try various interventions to prevent the criminally inclined from harming others?
What is the point of prison? This is itself no easy question, and it's one with a rich philosophical debate. Surely one of the biggest reasons is to protect society by preventing criminals from reoffending. This might be achievable by manipulating a felon's serotonin levels, but why not go even further?
Today, we know enough about the brain to have identified a very particular part of the prefrontal cortex responsible for aggressive behavior. We know that certain abnormalities in the amygdala can result in anti-social behavior and rule breaking. If the purpose of the penal system is to rehabilitate, then why not "edit" these parts of the brain in some way? This could be done in a variety of ways.
Credit: Otis Historical Archives National Museum of Health and Medicine via Flickr / Wikipedia
Electroconvulsive therapy (ECT) is a surprisingly common practice in much of the developed world. Its supporters say that it can help relieve major mental health issues such as depression or bipolar disorder as well as alleviate certain types of seizures. Historically, and controversially, it has been used to "treat" homosexuality and was used to threaten those misbehaving in hospitals in the 1950s (as notoriously depicted in One Flew Over the Cuckoo's Nest). Of course, these early and crude efforts at ECT were damaging, immoral, and often left patients barely able to function as humans. Today, neuroscience and ECT are much more sophisticated. If we could easily "treat" those with aggressive or anti-social behavior, then why not?
Ideally, we might use techniques such as ECT or hormonal supplementation, but failing that, why not go even further? Why not perform a lobotomy? If the purpose of the penal system is to change the felon for the better, we should surely use all the tools at our disposal. With one fairly straightforward surgery to the prefrontal cortex, we could turn a violent, murderous criminal into a docile and law-abiding citizen. Should we do it?
Is free will worth it?
As Burgess, who penned A Clockwork Orange, wrote, "Is a man who chooses to be bad perhaps in some way better than a man who has the good imposed upon him?"
Intuitively, many say yes. Moral decisions must, in some way, be our own. Even if we know that our brains determine our actions, it's still me who controls my brain, no one else. Forcing someone to be good, by molding or changing their brain, is not creating a moral citizen. It's creating a law-abiding automaton. And robots are not humans.
And yet, it begs the question: is "free choice" worth all the evil in the world?
If my being brainwashed or "rehabilitated" means children won't die malnourished or the Holocaust would never happen, then so be it. If lobotomizing or neuro-editing a serial killer will prevent them from killing again, is that not a sacrifice worth making? There's no obvious reason why we should value free will above morality or the right to life. A world without murder and evil — even if it meant a world without free choices for some — might not be such a bad place.
As Fyodor Dostoyevsky wrote in The Brothers Karamazov, if the "entrance fee" for having free will is the horrendous suffering we see all around us, then "I hasten to return my ticket." Free will's not worth it.
Do you think the Ludovico technique from A Clockwork Orange is a great idea? Should we turn people into moral citizens and shape their brains to choose only what is good? Or is free choice more important than all the evil in the world?
A new study suggests that private prisons hold prisoners for a longer period of time, wasting the cost savings that private prisons are supposed to provide over public ones.
- Private prisons in Mississippi tend to hold prisoners 90 days longer than public ones.
- The extra days eat up half of the expected cost savings of a private prison.
- The study leaves several open questions, such as what affect these extra days have on recidivism rates.
The United States of America, land of the free, is home to 5 percent of the world's population but 25 percent of its prisoners. The cost of having so many people in the penal system adds up to $80 billion per year, more than three times the budget for NASA. This massive system exploded in size relatively recently, with the prison population increasing by six-fold in the last four decades.
Ten percent of these prisoners are kept in private prisons, which are owned and operated for the sake of profit by contractors. In theory, these operations cost less than public prisons and jails, and states can save money by contracting them to incarcerate people. They have a long history in the United States and are used in many other countries as well.
However, despite the pervasiveness of private contractors in the American prison system, there is not much research into how well they live up to their promise to provide similar services at a lower cost to the state. The little research that is available often encounters difficulties in trying to compare the costs and benefits of facilities with vastly different operations and occasionally produces results suggesting there are few benefits to privatization.
A new study by Dr. Anita Mukherjee and published in the American Economic Journal: Economic Policy joins the debate with a robust consideration of the costs and benefits of private prisons. Its findings suggest that some private prisons keep people incarcerated longer and save less money than advertised.
The study focuses on prisons in Mississippi. Despite its comparatively high rate of incarceration, Mississippi's prison system is very similar to that of other states that also use private prisons. Demographically, its system is representative of the rest of the U.S. prison system, and its inmates are sentenced for similar amounts of time.
The state attempts to get the most out of its privatization efforts, as a 1994 law requires all contracts for private prisons in Mississippi to provide at least a 10 percent cost savings over public prisons while providing similar services. As a result, the state seeks to maximize its savings by sending prisoners to private institutions first if space if available.
While public and private prisons in Mississippi are quite similar, there are a few differences that allow for the possibility of cost savings by private operators — not the least of which is that the guards are paid 30 percent less and have fewer benefits than their publicly employed counterparts.
The results of privatization
The graph depicts the likelihood of release for public (dotted line) vs. private (solid line) prison inmates. At every level of time served, public prisoners were more likely to be released than private prisoners.Dr. Anita Mukherjee
The study relied on administrative records of the Mississippi prison system between 1996 and 2013. The data included information on prisoner demographics, the crimes committed, sentence lengths, time served, infractions while incarcerated, and prisoner relocation while in the system, including between public and private jails. For this study, the sample examined was limited to those serving between one and six years and those who served at least a quarter of their sentence. This created a primary sample of 26,563 bookings.
Analysis revealed that prisoners in private prisons were behind bars for four to seven percent longer than those in public prisons, which translates to roughly 85 to 90 extra days per prisoner. This is, in part, because those in private prison serve a greater portion of their sentences (73 percent) than those in public institutions (70 percent).
This in turn might be due to the much higher infraction rate in private prisons compared to public ones. While only 18 percent of prisoners in a public prison commit an infraction, such as disobeying a guard or possessing contraband, the number jumps to 46 percent in a private prison. Infractions can reduce the probability of early release or cause time to be added to a sentence.
It's unclear why there are so many more infractions in private prisons. Dr. Mukherjee suggests it could be the result of "harsher prison conditions in private prisons," better monitoring techniques, incentives to report more of them to the state before contract renewals, or even a lackadaisical attitude on the part of public prison employees.
What does all this cost Mississippi?
The extra time served eats 48 percent of the cost savings of keeping prisoners in a private facility. For example, it costs about $135,000 to house a prisoner in a private prison for three years and $150,000 in the public system. But longer stays in private prisons reduce the savings from $15,000 to only $7,800.
As Dr. Mukherjee remarks, this cost is also just the finance. Some things are a little harder to measure:
"There are, of course, other costs that are difficult to quantify — e.g., the cost of injustice to society (if private prison inmates systematically serve more time), the inmate's individual value of freedom, and impacts of the additional incarceration on future employment. Abrams and Rohlfs (2011) estimates a prisoner's value of freedom for 90 days at about $1,100 using experimental variation in bail setting. Mueller-Smith (2017) estimates that 90 days of marginal incarceration costs about $15,000 in reduced wages and increased reliance on welfare. If these social costs were to exceed $7,800 in the example stated, private prisons would no longer offer a bargain in terms of welfare-adjusted cost savings."
It is possible that the extra time in jail provides benefits that counter these costs, such as a reduced recidivism rate, but this proved difficult to determine. Though it was not statistically significant, there was some evidence that the added time actually increased the rate of recidivism. If that's true, then private prisons could be counterproductive.
Humans may have evolved to be tribalistic. Is that a bad thing?
- From politics to every day life, humans have a tendency to form social groups that are defined in part by how they differ from other groups.
- Neuroendocrinologist Robert Sapolsky, author Dan Shapiro, and others explore the ways that tribalism functions in society, and discuss how—as social creatures—humans have evolved for bias.
- But bias is not inherently bad. The key to seeing things differently, according to Beau Lotto, is to "embody the fact" that everything is grounded in assumptions, to identify those assumptions, and then to question them.
With the rise of Big Data, methods used to study the movement of stars or atoms can now reveal the movement of people. This could have important implications for cities.
- A treasure trove of mobility data from devices like smartphones has allowed the field of "city science" to blossom.
- I recently was part of team that compared mobility patterns in Brazilian and American cities.
- We found that, in many cities, low-income and high-income residents rarely travel to the same geographic locations. Such segregation has major implications for urban design.
Almost 55 percent of the world's seven billion people live in cities. And unless the COVID-19 pandemic puts a serious — and I do mean serious — dent in long-term trends, the urban fraction will climb almost to 70 percent by midcentury. Given that our project of civilization is staring down a climate crisis, the massive population shift to urban areas is something that could really use some "sciencing."
Is urbanization going to make things worse? Will it make things better? Will it lead to more human thriving or more grinding poverty and inequality? These questions need answers, and a science of cities, if there was such a thing, could provide answers.
Good news. There already is one!
The science of cities
With the rise of Big Data (for better or worse), scientists from a range of disciplines are getting an unprecedented view into the beating heart of cities and their dynamics. Of course, really smart people have been studying cities scientifically for a long time. But Big Data methods have accelerated what's possible to warp speed. As "exhibit A" for the rise of a new era of city science, let me introduce you to the field of "human mobility" and a new study just published by a team I was on.
Credit: nonnie192 / 405009778 via Adobe Stock
Human mobility is a field that's been amped up by all those location-enabled devices we carry around and the large-scale datasets of our activities, such as credit card purchases, taxi rides, and mobile phone usage. These days, all of us are leaving digital breadcrumbs of our everyday activities, particularly our movements around towns and cities. Using anonymized versions of these datasets (no names please), scientists can look for patterns in how large collections of people engage in daily travel and how these movements correlate with key social factors like income, health, and education.
There have been many studies like this in the recent past. For example, researchers looking at mobility patterns in Louisville, Kentucky found that low-income residents tended to travel further on average than affluent ones. Another study found that mobility patterns across different socioeconomic classes exhibit very similar characteristics in Boston and Singapore. And an analysis of mobility in Bogota, Colombia found that the most mobile population was neither the poorest nor the wealthiest citizens but the upper-middle class.
These were all excellent studies, but it was hard to make general conclusions from them. They seemed to point in different directions. The team I was part of wanted to get a broader, comparative view of human mobility and income. Through a partnership with Google, we were able to compare data from two countries — Brazil and the United States — of relatively equal populations but at different points on the "development spectrum." By comparing mobility patterns both within and between the two countries, we hoped to gain a better understanding of how people at different income levels moved around each day.
Mobility in Brazil vs. United States
Socioeconomic mobility "heatmaps" for selected cities in the U.S. and Brazil. The colors represent destination based on income level. Red depicts destinations traveled by low-income residents, while blue depicts destinations traveled by high-income residents. Overlapping areas are colored purple.Credit: Hugo Barbosa et al., Scientific Reports, 2021.
The results were remarkable. In a figure from our paper (shown above), it's clear that we found two distinct kinds of relationship between income and mobility in cities.
The first was a relatively sharp distinction between where people in lower and higher income brackets traveled each day. For example, in my hometown of Rochester, New York or Detroit, the places visited by the two income groups (e.g., job sites, shopping centers, doctors' offices) were relatively partitioned. In other words, people from low-income and high-income neighborhoods were not mixing very much, meaning they weren't spending time in the same geographical locations. In addition, lower income groups traveled to the city center more often, while upper income groups traveled around the outer suburbs.
The second kind of relationship was exemplified by cities like Boston and Atlanta, which didn't show this kind of partitioning. There was a much higher degree of mixing in terms of travel each day, indicating that income was less of a factor for determining where people lived or traveled.
In Brazil, however, all the cities showed the kind of income-based segregation seen in U.S. cities like Rochester and Detroit. There was a clear separation of regions visited with practically no overlap. And unlike the U.S., visits by the wealthy were strongly concentrated in the city centers, while the poor largely traversed the periphery.
Data-driven urban design
Our results have straightforward implications for city design. As we wrote in the paper, "To the extent that it is undesirable to have cities with residents whose ability to navigate and access resources is dependent on their socioeconomic status, public policy measures to mitigate this phenomenon are the need of the hour." That means we need better housing and public transportation policies.
But while our study shows there are clear links between income disparity and mobility patterns, it also shows something else important. As an astrophysicist who spent decades applying quantitative methods to stars and planets, I am amazed at how deep we can now dive into understanding cities using similar methods. We have truly entered a new era in the study of cities and all human systems. Hopefully, we'll use this new power for good.