Passing over the infancy of Rome, the two principal walls that succeeded are that of Servius Tullius, and that of Aurelian. The first was built about two centuries after the town had its origin. It included the Capitol, Viminal, Quirinal, Esquiline, Palatine, Celian, and Aventine, or the Seven Hills of Rome, with a small triangular piece of ground on the other side of the Tiber, which did not, however, include the present site of St. Peter’s. The space within these limits, would not exceed that which is now covered by New York, below Bleecker street, and yet it was the Rome of the Augustan age. The hills are not large, though some are double the size of others. The Capitol and Palatine are both small, particularly the former, which, agreeably to our mode of constructing, could not hold a population to exceed two or three thousand, even with narrow streets with high houses. Admitting the lowest numbers that are given as the population of Rome at this period, it is difficult to imagine where they all lived. Pompeii proves that the Romans did not personally occupy much space, although the courts and gardens did. The slaves, who must have composed a large portion of the population of Rome, were probably crowded into a small space; and the great depth of the _débris_ that now covers the ancient city proves that the materials were abundant: from all which it is fair to infer that the dwellings were of great height. The houses around Naples were low, probably on account of frequent earthquakes, calamities that doubtless occurred oftener before the great eruption of the volcano than since. After making all these allowances, however, it will be necessary to people suburbs of great extent, or to diminish, by more than half, the popular accounts of the number of the inhabitants. The emperor Aurelian, fearful that the town might be taken by surprise, on account of the extent of the suburbs, about the year 276, caused new walls to be built. These walls in no place touched the wall of Servius Tullius, and may have a little more than doubled the size of the _enceinte_. These walls still exist, or, at least, walls exist that are attributed equally to Aurelian and Honorius, who lived more than a century later. Some of the antiquaries contend that the walls of Aurelian included a space more than twice, or even thrice as great as that contained within the present walls, and thus account for the mode of accommodating the population, which they complacently take at the highest number. A writer, who was a contemporary of Aurelian, affirms that the wall of this emperor was fifty miles in circuit; and Vasi appears to adopt his account of the matter, though he is obliged to admit that no traces exist of these prodigiously extensive works.