PELSO(Aur. Vict. de Caes. 40) or PEISO (Plin. Nat. 3.27), a considerable lake in the north of Pannonia. A large portion of it was drained by the emperor Galerius, who conducted its waters into the Danube, and thus reclaimed large tracts of land, which formed an important addition to the province. (Aur. Vict. l. c.) The modern name of this lake is Plattensee:during rainy seasons it still overflows its banks far and wide, and forms extensive marshes, which are probably the very districts that were drained by Galerius. Lake Pelso is mentioned under different modifications of this name, such as Lacus Pelsodis (Jornand. Get. 52, 53) and Pelsois (Geogr. Rav. 4.19), while in the middle ages it was called Pelissa. Muchar ( Noric. 1. p. 3, &c.) regards Peiso and Pelso as two lakes, placing the former, with Pliny, near the Deserta Boiorum, and identifying it with the Neusiedlersee, while he admits the Pelso to be the Plattensee. This hypothesis, however, can hardly be sustained, as it is pretty certain that the Neusiedlerseedid not exist in the times of the Romans, but was formed at a later period. (Comp. Scheonwisner, Antiquitates et Historia Sabariae, p. 17, &c. Liechtenberg, Geogr. des Oester. Kaiserstaates, vol. 3. p. 1245, &c.)
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