In Pliny (iii. 9), we meet with the strange expression: _Moenia ejus collegere ambitu Imperatoribus Censoribusque Vespasianis, anno conditae DCCCXXVII. pass. XIIIMCC._, an expression which proves in a striking manner that an accurate knowledge of language and etymology cannot be dispensed with, even in matters which we observe with our own eyes. It has been unjustly inferred from this passage, that in the reign of Vespasian Rome was provided with walls, and those, too, of a much wider circumference than those of Servius. This arose from ignorance of the fact that, according to the most ancient Roman usage, _moenia_ always signifies “buildings.” In like manner, Virgil’s expression, _Dividimus muros et moenia pandimus urbis_, contains no tautology, as was well-known to the ancient grammarians, for the meaning is: “we break the walls, and thereby lay open the buildings of the city.” So also Florus, who sometimes follows the ancient usage, says: _hic igitur et moenia muro amplexus_. We must accordingly understand the passage of Pliny as comprising the whole complex of Rome, as it was measured in the time of Vespasian, which, of course, is a variable magnitude. As it is generally understood, the expression would be as absurd, as if I were to say: the walls of the city of Cologne, in 1828, were of such or such an extent, having, of course, had the same circumference two hundred years ago. Rome had long since been extended beyond the ancient walls, which were now, in fact, in the midst of the city; the towers had been taken down, and people built houses there, the interdicts against building on the pomoerium being no longer attended to. In like manner the foundations of the ancient walls of London may still be discerned among the houses. From Frontinus’ work on Aqueducts, we see how, though the police was excellent, abuses had crept in, although not as many as at present, because the lower administration was not carried on in so servile a manner; when an experienced man was entrusted with the superintendence, things went on fairly, but if not, every one took the greatest liberty. Such was the case at Rome, until Frontinus came forward as a reformer. The disorder was then so great that any one built a house wherever he pleased, without asking whether he had a right to do so or not; and hence the city ever continued to extend. I have made a series of observations on the origin of particular buildings, in order to see approximately, how the city became enlarged under the several emperors. In the reign of Augustus, the Campus Martius was principally chosen for the erection of large buildings: there Agrippa built his Thermae and the Pantheon, and Augustus his Mausoleum; for the Campus was no longer the plain for reviewing the citizens, nor were the mock-comitia of the centuries held there any longer, but it was confined to a small plain near the river, as may be seen from Pliny’s panegyric on Trajan. This part of the Campus,