Beyond this there was a settlement on the Carinæ, the farthest summit of the Esquiline, with the fortress for defence against the Sabines in the valley of the Subura; this afterwards became the second Servian quarter. At that time the Esquiliæ (which did not properly speaking include the Carinæ) formed, as the name signifies, a suburb (_exquiliæ_, the same as _inquilinus_). That the town should have extended itself in this direction is explained by the simple fact that the people remained on the heights, especially on the Palatine and the Velian, avoiding both the isolated hills and the swampy and wholly defenceless valleys which lay between. At a later time the suburb was included in the town, and under the Servian division it became the third quarter. The “bridge of piles” (_pons sublicius_) thrown across that natural pier, the island in the Tiber, and the _tête de pont_ on the Etruscan shore, the citadel of the Janiculum, remained outside the fortifications of the “Seven Hills.” And as, for military reasons, it was necessary to be able to break down or burn the bridge at the shortest notice, there arose a fixed rule which down to a very late period was observed as a traditional religious law, that no iron could be used in the construction of the bridge, but only wood. Thus a town came into being, but nevertheless the real and complete amalgamation of the various bodies which formed the settlement was not yet effected. As there was no common city altar, but the separate altars of the different curies merely stood side by side in the same neighbourhood, so not only did the distinction between citadel and town continue, but the seven circles themselves were rather a collection of urban settlements than a united town until the gigantic defensive works, ascribed to King Servius Tullius, surrounded the inner and outer city and the open suburbs with a single great wall. But before these strong works were set in hand, the position of Rome in relation to the surrounding district had doubtless entirely changed. As the primitive uncommercial and inactive epoch of the Latin stock corresponds to the period in which the husbandman drove the plough on the Palatine as well as over the other hills of Latium, and the place of refuge on the Capitol, which in ordinary times stood empty, presented only the commencement of a fortified settlement; and as later the flourishing settlement on the Palatine and within the seven circles coincides with the occupation of the estuary of the Tiber by a Roman community and generally with the progress of the Latins to a free and active intercourse, and urban civilisation especially in Rome, and indeed to a firmer political consolidation both of the separate states and of the confederacy; so does the establishment of a single great city by means of the Servian rampart belong to that epoch in which the city of Rome was enabled to contend for the supremacy of the Latin confederacy and finally to get the upper hand.[c]