The origin of the name, Pisa, is a mystery. While the origin of the city had remained unknown for centuries, the Pelasgi, the Greeks, the Etruscans, and the Ligurians had variously been proposed as founders of the city (for example, a colony of the ancient city of Pisa, Greece). Archaeological remains from the fifth century BC confirmed the existence of a city at the sea, trading with Greeks and Gauls. The presence of an Etruscan necropolis, discovered during excavations in the in 1991, confirmed its Etruscan origins.