The first settlements built in the area are of Venetic origin, during the twelfth to ninth centuries BC, consisting of stilt houses in the wetlands, that were then still close to the sea. At that time the main stream of the Po, the Adria channel, flowed into the sea in this area. The Villanovan culture, named for an archaeological site at the village of Villanova, near Bologna (Etruscan Felsina), flourished in this area from the tenth until as late as the sixth century BC. The foundations of classical Atria are dated from 530 to 520 BC.
The Etruscans built the port and settlement of Adria after the channel gradually started to run dry. During the later period of the sixth century BC the port continued to flourish. The Etruscan-controlled area of the Po Valley was generally known as Padanian Etruria, as opposed to their main concentration along the Tyrrhenian coast south of the Arno.
Greeks from Aegina and later from Syracuse by Dionysius I colonised the city making it into an emporion. Greeks had been trading with the Veneti from the sixth century BC at least, especially the amber, originally coming from the Baltic sea.
Source: Adria – Wikipedia