Strabo Geography 5.1.7

[7] These cities are situated high above the marshes; near to them is Patavium, ¹ the finest of all the cities in this district, and which at the time of the late census ² was said to contain 500 equites. Anciently it could muster an army of 120,000 men. The population and skill of this city is evinced by the vast amount of manufactured goods it sends to the Roman market, especially clothing of all kinds. It communicates with the sea by a river navigable from a large harbour [at its mouth], the river runs across the marshes for a distance of 250 stadia. This harbour, ³ as well as the river, ⁴ is named Medoacus. Situated in the marshes is the great [city of] Ravenna, built entirely on piles, ⁵ and traversed by canals, which you cross by bridges or ferry-boats. At the full tides it is washed by a considerable quantity of sea-water, as well as by the river, and thus the sewage is carried off, and the air purified; in fact, the district is considered so salubrious that the [Roman] governors have selected it as a spot to bring up and exercise the gladiators in. It is a remarkable peculiarity of this place, that, though situated in the midst of a marsh, the air is perfectly innocuous; the same is the case with respect to Alexandria in Egypt, where the malignity of the lake during summer is entirely removed by the rising of the river which covers over the mud. Another remarkable peculiarity is that of its vines, which, though growing in the marshes, make very quickly and yield a large amount of fruit, but perish in four or five years. Altinum ⁶ stands likewise in the marshes, its situation being very similar to that of Ravenna. Between them is Butrium, ⁷ a small city of Ravenna, and Spina, ⁸ which is now a village, but was anciently a celebrated Grecian city. In fact, the treasures of the Spinitae are shown at Delphi, and it is, besides, reported in history that they had dominion over the sea. They say that it formerly stood on the sea; now, however, the district is inland about 90 stadia from the sea. Ravenna is reported to have been founded by Thessalians, who not being able to sustain the violence of the Tyrrheni, welcomed into their city some of the Ombrici, who still possess it, while they themselves returned home. These cities for the most part are surrounded, and, as it were, washed by the marshes.