The Insulae: How Rome Housed Its Millions
The city of Rome at its height had a population of somewhere between half a million and a million people — the estimates vary and the ancient census figures are difficult to interpret — compressed into an urban area that had no master plan, no grid, and no effective building code until the fires that made such codes politically possible. The vast majority of these people lived not in the marble houses of imperial imagination but in multi-story apartment buildings called insulae — islands — so called because they filled city blocks the way islands fill water, surrounded on all sides by streets. The insula was Rome’s residential reality, and it was often dangerous, frequently squalid, and occasionally catastrophically flammable.
The insulae ranged in quality from buildings that would be recognizable as respectable urban apartments to structures so poorly built and so overcrowded that they collapsed with some regularity. Roman law periodically set height limits — Augustus at twenty meters, later reduced — and Roman writers commented on the engineering deficiencies of insulae with the casual familiarity of people who lived near them. Juvenal, the satirist, listed the risk of falling buildings alongside fire and street crime as standard hazards of Roman urban life. The upper floors were cheapest — no elevator, shared latrines, no running water, greatest risk of fire and structural failure — and housed the poorest residents. The ground floor, with street access and sometimes its own latrine, commanded higher rents and housed small businesses, workshops, and better-off tenants.
Water was a defining constraint of insular life. The aqueducts that delivered hundreds of millions of liters of water daily to Rome distributed it through a hierarchical system: the largest users — baths, imperial buildings, fountains — took priority. Private households could pay for water connections, but most insulae did not have them. The practical implication was that most residents of the upper floors obtained their water from fountains at street level, carried it up in containers, and disposed of waste in chamber pots that were either emptied into street gutters or, if the building lacked courtyard facilities, thrown out windows. Roman law imposed penalties for throwing things from windows that struck passers-by, which is the kind of law that only gets written because the practice was common enough to require regulation.
Fire was the existential threat. Roman construction used timber extensively — floors, roof structures, internal partitions — and the densely packed insulae with their open cooking fires and oil lamps constituted a fire risk that the city’s geography, with its narrow streets and close-packed blocks, made very difficult to manage. Rome suffered catastrophic fires repeatedly, most famously the Great Fire of 64 AD that destroyed or damaged ten of the city’s fourteen administrative districts and that Nero used as the opportunity to build his Domus Aurea on the cleared land. Nero’s subsequent building regulations — wider streets, fireproof materials for ground floors, limitations on shared walls — were genuine attempts to address the structural fire risk, though the city’s growth and its housing pressures meant that enforcement was always imperfect.
The social geography of the insula was thoroughly mixed in ways that the geography of later European cities was not. The wealthiest residents lived at ground level; the poorest at the top. A single building might contain a wealthy merchant’s family on the ground floor, a series of middle-income tenants on the second and third floors, and extremely poor workers sharing single rooms on the upper floors. This vertical social stratification meant that Romans of different economic positions shared buildings, staircases, and courtyard facilities in daily proximity that later periods of urban development, with their horizontal social segregation into different neighborhoods, broke apart.
Outside the capital, the insulae were less dominant. Cities like Pompeii — with its eruption-frozen streetscape of relatively intact buildings — show a predominance of single-family domus, the courtyard houses that appear in the standard illustrations of Roman domestic life. The domus was the house of the property-owning classes: organized around an atrium, with a compluvium open to the sky, decorated with mosaics and frescoes, providing privacy and space that the insular apartment did not. The gap between the domus and the insula was the gap between the Roman who wrote about Roman life and the Roman who actually constituted it numerically. Most Romans lived in the insulae. Most Roman writing about domestic life describes the domus.
What Rome’s housing problem demonstrates is that the engineering and administrative capacity that produced the Colosseum and the aqueducts was not matched by any equivalent capacity to house the urban population safely. This is not a paradox. The Colosseum was built with state resources for state purposes. Housing was a private market, subject to the incentives of landlords who had no interest in expensive fireproofing and every interest in packing as many tenants as possible into buildings with minimal maintenance expenditure. The Roman state could build remarkable public infrastructure. It could not, or would not, impose the costs necessary to make private housing safe. This gap between public ambition and private squalor is one of the most recognizable things about Rome, and not only about Rome.