Strabo Geography 5.3.7

[7] In the interior, the first city above Ostia is Rome; it is the only city built on the Tiber. It has been remarked above, that its position was fixed, not by choice, but necessity; to this must be added, that those who afterwards enlarged it, were not at liberty to select a better site, being prevented by what was already built. The first [kings] fortified the Capitol, the Palatium, and the Collis Quirinalis, which was so easy of access, that when Titus Tatius came to avenge the rape of the [Sabine] virgins, he took it on the first assault. Ancus Marcius, who added Mount Caelius and the Aventine Mount with the intermediate plain, separated as these places were both from each other and from what had been formerly fortified, was compelled to do this of necessity; since he did not consider it proper to leave outside his walls, heights so well protected by nature, to whomsoever might have a mind to fortify themselves upon them, while at the same time he was not capable of enclosing the whole as far as Mount Quirinus. Servius perceived this defect, and added the Esquiline and Viminal hills. As these were both of easy access from without, a deep trench was dug outside them and the earth thrown up on the inside, thus forming a terrace of 6 stadia in length along the inner side of the trench. This terrace he surmounted with a wall flanked with towers, and extending from the Colline ¹ to the Esquiline gate. Midway along the terrace is a third gate, named after the Viminal hill. Such is the Roman rampart, which seems to stand in need of other ramparts itself. But it seems to me that the first [founders] were of opinion, both in regard to themselves and their successors, that Romans had to depend not on fortifications, but on arms and their individual valour, both for safety and for wealth, and that walls were not a defence to men, but men were a defence to walls. At the period of its commencement, when the large and fertile districts surrounding the city belonged to others, and while it lay easily open to assault, there was nothing in its position which could be looked upon as favourable; but when by valour and labour these districts became its own, there succeeded a tide of prosperity surpassing the advantages of every other place. Thus, notwithstanding the prodigious increase of the city, there has been plenty of food, and also of wood and stone for ceaseless building, rendered necessary by the falling down of houses, and on account of conflagrations, and of the sales, which seem never to cease. These sales are a kind of voluntary falling down of houses, each owner knocking down and rebuilding one part or another, according to his individual taste. For these purposes the numerous quarries, the forests, and the rivers which convey the materials, offer wonderful facilities. Of these rivers, the first is the Teverone, ² which flows from Alba, a city of the Latins near to the country of the Marsi, and from thence through the plain below this [city], till it unites with the Tiber. After this come the Nera ³ and the Timia, ⁴ which passing through Ombrica fall into the Tiber, and the Chiana, ⁵ which flows through Tyrrhenia and the territory of Clusiumn. ⁶ Augustus Caesar endeavoured to avert from the city damages of the kind alluded to, and instituted a company of freedmen, who should be ready to lend their assistance in cases of conflagration; ⁷ whilst, as a preventive against the falling of houses, he decreed that all new buildings should not be carried so high as formerly, and that those erected along the public ways should not exceed seventy feet in height. ⁸ But these improvements must have ceased only for the facilities afforded by the quarries, the forests, and the ease of transport.