In the 8th century BC, the Etruscans expanded their power to Northern and Southern Italy, specifically towards Emilia and Campania, there they founded Etruscan dominions who are modernly known under the names of Padanian Etruria and Campanian Etruria. Moving from the northern city-states of the Tuscanian Dodecapolis they swept into the Po valley through the Apennine passes.
The Greek and Latin ancient writers tell us that an Etruscan expansion into Southern Italy, present day Campania region, and northwards into the Po Valley occurred yet in the 9th century BC.
Following their usual methods, the Etruscan conquerors in the colonial areas overlapped themselves over the ancient inhabitants of the conquered regions imposing their culture and their political institutions. Consequently, as in Tuscany, the cities they founded in the Po valley and along the Adriatic coast formed a Dodecapolis (a federation or league of twelve cities), but, as for the original Tuscanian Dodecapolis, we do not really know which cities were part of it. Inside Padanian Etruria, it is supposed they were ‘’Felsina’’ (Bologna), Spina and Marzabotto, while we can only guess about Ravenna, Cesena, Rimini, Modena, Parma, Piacenza, Mantua and possibly, but improbably, Milan.
The founder of these cities and of their League had been Ocnus, brother or son of Aulestes (or Auletes), according some authors, Tarchon according others. More probably, as the archaeological evidence suggests, both the traditions have to be accepted but must also be ascribed to two different moments of profound change in the political and economic framework of the Padanian Etruria.
A "First etruscan colonization," referred to the legendary Tarchon, can be traced to the early Iron Age (9th century BC). It was aimed to find new lands for agricultural uses; a "Second colonization", dated to the mid-6th century BC, can be attributed to the as much legendary Ocnus. The latter colonization involved the reorganization of the entire Padanian region in order to increase its utility for the etruscan businesses and trades.