The most diligent researches have collected only the following circumstances; which, slight and imperfect as they are, may tend, in some degree, to illustrate the question of the populousness of ancient Rome.

I.When the capital of the empire was besieged by the Goths, the circuit of the walls was accurately measured, by Ammonius, the mathematician, who found it equal to twenty-one miles.
It should not be forgotten that the form of the city was almost that of a circle; the geometrical figure which is known to contain the largest space within any given circumference.II.The architect Vitruvius, who flourished in the Augustan age, and whose evidence, on this occasion, has peculiar weight and authority, observes, that the innumerable habitations of the Roman people would have spread themselves far beyond the narrow limits of the city; and that the want of ground, which was probably contracted on every side by gardens and villas, suggested the common, though inconvenient, practice of raising the houses to a considerable height in the air.

But the loftiness of these buildings, which often consisted of hasty work and insufficient materials, was the cause of frequent and fatal accidents; and it was repeatedly enacted by Augustus, as well as by Nero, that the height of private edifices within the walls of Rome, should not exceed the measure of seventy feet from the ground.III.Juvenal laments, as it should seem from his own experience, the hardships of the poorer citizens, to whom he addresses the salutary advice of emigrating, without delay, from the smoke of Rome, since they might purchase, in the little towns of Italy, a cheerful commodious dwelling, at the same price which they annually paid for a dark and miserable lodging.

House-rent was therefore immoderately dear: the rich acquired, at an enormous expense, the ground, which they covered with palaces and gardens; but the body of the Roman people was crowded into a narrow space; and the different floors, and apartments, of the same house, were divided, as it is still the custom of Paris, and other cities, among several families of plebeians.IV.The total number of houses in the fourteen regions of the city, is accurately stated in the description of Rome, composed under the reign of Theodosius, and they amount to forty-eight thousand three hundred and eighty-two.

The two classes of _domus_ and of _insul_, into which they are divided, include all the habitations of the capital, of every rank and condition from the marble palace of the Anicii, with a numerous establishment of freedmen and slaves, to the lofty and narrow lodging-house, where the poet Codrus and his wife were permitted to hire a wretched garret immediately under the files.