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 fluviatile" may reach a carapace length of , with females being generally smaller than males. As with other crabs, the body is roughly square, with the reduced abdomen tucked beneath the thorax. The thorax bears five pairs of legs, the first of which is armed with large claws. The life span of "P. fluviatile" is typically 10–12 years. Moulting does not occur in winter. Mating lasts between 30 min and 21 hours, with spawning usually taking place in August. Females carry the eggs on their pleopods (appendages on the abdomen) until they hatch directly into juvenile crabs, having passed through