In the Eastern Liguria territory known as marca Obertenga, Otto returned Oberto Obizzo to his lands and appointed him the margrave of the newly created March of Genoa.

About 1133 Rainier's son Marquess William V married Judith of Babenberg, a half-sister of King Conrad III of Germany, and so greatly increased his family's prestige.

He entered into the Italian policies of Conrad and the Byzantine Emperor Manuel I Komnenos, setting a Ghibelline precedent for his successors, and with his sons became involved in the Crusades.

It had to wage several long wars against the independence-minded communes of Asti and Alessandria and it became the standard-bearer of a renewed Lombard League which was forged to fight the spread of Angevin influence into northern Italy.

His son Margrave William X was elevated to a Duke of Montferrat in 1574 and the "march" ceased to exist as an entity, though it had already undergone the significant change from a feudal collection of frontier counties to one of the petty states of Renaissance Italy, divided into two separated territories.