The Ravenna that Augustus thus chose to be the great base and port of his fleet in the eastern sea was, as we have seen, a place built upon piles in the midst of the marshes, impregnable from the land, and, because impregnable, able, whenever it was in dispute, to command the narrow pass between the mountains and the sea that was the gate of Italy and Cisalpine Gaul. Such a place, situated as it was upon the western shore of that sea which was the fault between East and West, was eminently suitable for the great purpose of the emperor. Pliny[1] indeed would seem to tell us that from time immemorial Ravenna had possessed a small port; but such a place, well enough for the small traders of those days, could not serve usefully the requirements of a great fleet. Therefore the first act of Augustus, when he had chosen Ravenna as his naval base, was the construction of a proper port and harbour, and these came to be named, after the fleet they served and accommodated, Classis. Classis was situated some two and a half miles from the town of Ravenna to the east-south-east. We may perhaps have some idea both of its situation and of its relation to Ravenna if we say that it was to that city what the Porto di Lido is to Venice. [Footnote 1: Pliny, iii. 20; cf. also Strabo, v. 7.] It is very difficult, in looking upon Ravenna as we see it to-day, to reconstruct it, even in the imagination, as it was when Augustus had done with it. To begin with, the sea has retreated several miles from the city, which is no longer within sight of it, while all that is left of Classis, which is also now out of sight of the sea, is a single decayed and deserted church, S. Apollinare in Classe. Strabo, however, who wrote his _Geography_ a few years after Augustus had chosen Ravenna for his port upon the Adriatic, has left us a description both of it and the country in which it stood, from which must be drawn any picture we would possess of so changed a place. He speaks of it, as we have seen, as "a great city" situated in the marshes, built entirely upon piles, and traversed by canals which were everywhere crossed by bridges or ferry-boats. While at the full tide he tells us it was swept by the sea and always by the river, and thus the sewage was carried off and the air purified, and this so thoroughly, that even before its establishment by Augustus the district was considered so healthy that the Roman governors had chosen it as a spot in which to train gladiators.[1] That river we know from Pliny[2] was called the Bedesis; and the same writer tells us that Augustus built a canal which brought the water of the Po to Ravenna. [Footnote 1: Strabo, v. 7.] [Footnote 2: Pliny, iii. 20.]