The Etruscans were a diachronically continuous population, with a distinct language and culture during the period of earliest European writing, in the Mediterranean Iron Age in the second half of the first millennium BCE. They ranged over the Po Valley and some of its alpine slopes, southward along the west coast of Italy, most intensely in Eturia with enclaves as far south as Campania, and inland into the Appennine mountains. Their prehistory can be traced with certainty to about 1000 BCE. At their height about 500 BCE, they were a significant maritime power with a presence in Sardinia and the Aegean Sea.