The first document that speaks of this place is of 1176 and describes Gradisca as a farming village of seven families, some of Slavic origin, some Latin, under the jurisdiction of the patriarch of Aquileia. Then history says nothing for three hundred years. In the second half of the fifteenth century Venice refounded the village inside a fortress, as a bulwark against the Turkish raids: the whole town was shut inside a wall almost twenty metres high, strengthened by seven towers, and outside the walls the waters of the Isonzo were diverted into a wide defensive ditch. The outpost mattered enough that in 1500 the Venetian Senate sent Leonardo da Vinci here, to devise new weapons and new systems of defence; today at the entrance of Porta Nuova there is a bust of him. When the fortress was founded there was a thought of renaming the town Emopoli, in honour of the Venetian captain Giovanni Emo, but the new name did not take and the old Slavic one stayed: gradišče, the fortified place.
In 1511 the troops of Maximilian I besieged and bombarded the town, which held out long and gave in only when plague broke out inside the walls. A century later Venice tried to take it back and failed, in a war that carries the town's name; at the end Gradisca became the capital of a county of its own, which the emperor sold to a prince of the Eggenberg to meet the expenses of the Thirty Years' War. From 1647 the fifty-two localities of that county behaved like a small autonomous state, with a flourishing economy and a considerable independence from imperial power even in matters of law, of coinage and of weights and measures. Then the male line of the Eggenberg died out, Maria Theresa merged Gradisca with Gorizia, and in 1788 the town became a bishop's seat, with jurisdiction over Gorizia itself. In the house of the Venetian provveditori, since 1965, is the first public regional wine cellar in Italy.