Umag was mentioned for the first time in the 7th century by an anonymous citizen from Ravenna, but had already existed in Roman times. Proof of that is found in the numerous remains of Roman retreats, the so-called villa rustica uncovered all along the coast. The town's history is closely linked to the settlement of Sipar whose ruins can be found on the narrow cape, six kilometres north of Umag. In the 9th century the fortified settlement of Sipar was devastated by invaders, the Neretva pirates. However, after this unfortunate incident Umag grew in significance thanks also to its location, a small islet separated from the mainland with a narrow channel. It was actually this location to safeguard the settlement from the continuous invasions throughout the centuries. The Roman period of relative prosperity was substituted by one of insecurity caused primarily by frequent invasions, outbreaks of plague, cholera, and malaria. The number of its dwellers declined rapidly. Umag became part of the reigns of Odoacre, Theodoric and was ruled by the Longobards too.
From 6th to 8th centuries it fell under Byzantine dominion, followed by the rule of the Lombards in 751 and Francs in 774. The period to come was marked by insecurity and frequent changes of government from the Patriarchs of Grado and Aquileia to the Bishops of Trieste. However, the increasingly powerful Venetian Republic imposed its rule over Istria forcing Umag and other western Istrian towns to swear loyalty to Venice. Actually, in 1269 the Commune of Umag promised loyalty to Venice which from that time all through 1797 was to appoint governors of Umag from among its nobility. This period was by no means a peaceful one.
Century old clashes with Genoa brought about more destruction and looting. In 1370 the Genovese navy attacked Umag destroying the town's archive. The outbreaks of plague that decimated the dwellers forced the Venetian authorities to consider colonising the area with new settlers,
