Speculative building - putting up an apartment building or houses in the hope of finding and fleecing renters or buyers - is far from a modern phenomenon. I don't think that we can say when speculative building began; in some sense, the practice is probably almost as old as urbanization. We do know, however, where speculative building first flourished on a modern scale: the city of Rome.

From the mid-Republican period through the fourth century CE, Rome was the biggest, most notorious, and most dangerous city on the face of the earth. As the center of a Mediterranean-spanning empire, Rome's appeal was obvious. Juvenal famously complains about the hordes of Syrian immigrants, and a rich array of inscriptions in Greek, Syriac, and Hebrew attests to the teeming diversity of Rome's streets. To new migrants, the city's dangers may have been less evident: the thieves who waited in dark alleys at night, the grinding poverty that overtook those who failed to find a reliable occupation or patron, and - worst of all - the hyperendemic malaria that killed thousands every year. Rome's population was never able to reproduce itself; but the constant stream of migrants ensured that it remained more or less stable until the fourth century, when imperial patronage migrated elsewhere.

There was, in short, constant and reliable demand for housing in Rome. And there were plenty of aristocrats ready and willing to erect, derive rent from, and signally fail to maintain said housing. The vast majority of Romans lived in the apartment buildings called insulae ("islands"). These were multistory buildings, usually arranged around a central courtyard, with shops on the ground floor, "good" apartments on the story above, and increasingly unlivable units higher up. Although a series of emperors attempted to limit the height of insulae, the regulations applied only to street frontage, and unscrupulous contractors propped precarious additional stories on the roof. Some insulae, like the famous Insula Felicles by the Circus Maximus, must have approached the 170-foot height of the Colosseum.

Insulae (along with that safest of premodern investments, agricultural land) were recognized as a lucrative source of income by Roman investors. Cicero seems to have been something of a slumlord, and complains about the collapse of several of his units in a joking letter to Atticus. His tenants, one imagines, were less amused. The most famous real estate magnate in Roman history was doubtless the triumvir Crassus, who (as Plutarch tells us) liked to buy buildings when they were actually on fire (thus getting a much-reduced price from the despairing owner), send in highly-trained teams of slaves extinguish to the blaze and repair the structure, and "flip" the reconstructed insula as a rental property. Many less famous Romans got in on the rental game; the poet Martial reports that one wealthy notable derived a whopping three million sesterces each year from apartments in Rome and market gardens in the vicinity.

When a wealthy Roman decided to build an apartment building, he (or more likely, a trusted freedman) would contact one of Rome's contracting firms. These firms seem to have usually been relatively small, consisting of the contractor himself and a dozen or so skilled slaves or freedmen. Once the investor supplied the money, the contractor would hire as many unskilled laborers as he needed and set to work. Insulae - if we may extrapolate from the many well-preserved examples in Ostia (Rome's harbor) - were usually built (like most large Roman buildings) with walls of brick-faced concrete. Besides enabling the construction of soaring domes like the Pantheon's and vast vaults like those of the Baths of Caracalla, Roman concrete was a time-saver, allowing a few skilled workers to oversee the rapid construction of thick and solid walls. As long as the money kept flowing, a four- or five-story insula could thus be ready for occupation in a few months.

We know regrettably little about rents in Rome, save that they were usually regarded as extortionate. Rent was due once a year (on July 1), a time of great distress for poorer tenants; Martial devotes an epigram to a poor man evicted from his room and forced to live under a bridge. Like their modern counterparts, Roman apartments had managers (the same man, often a freedman, would manage all the buildings owned by a given investor), doormen (insularii), and remorseless rent collectors. Buildings were often known by the name of the owner, but were sometimes given alluring names (like Felicles - "Happy Isles") to allure renters.

The towering, tottering apartment blocks of Rome are merely the most modern-seeming of many premodern ventures into speculative construction. The basic phenomenon is as old as rent.