Potamon fluviatile as well as on the island of Sicily. Although it used to be found as far north as Lake Garda, "P. fluviatile" no longer occurs north of the River Po. In 1997 a population of "P. fluviatile" was discovered under the ruins of Trajan's Forum in the heart of Rome, living in canals built by the Etruscans which connect to the "Cloaca Maxima". Based on a genetic analysis, which demonstrated that these crabs were similar to those in Greece, researchers believe that they had been brought by the Greeks before the founding of the city, some 3000 years ago. The
Potamon fluviatile are right-handed. In the Tosco-Emilian Apennines, "P. fluviatile" is only found south of the watershed, in contrast with the crayfish "Austropotamobius pallipes", which occurs on both sides on the mountains. Although their ranges overlap, the two species do not inhabit the same water courses, apparently because the crab outcompetes the crayfish, which is therefore forced to live in less favourable locations where the crab cannot survive. Non-indigenous crayfish may pose a greater threat to "P. fluviatile" than native crayfish, although the greatest threats remain pollution, overfishing and the draining of wetlands. The natural range of "Potamon fluviatile" is highly fragmented,