Gradisca d'Isonzo (grädē`skä dēsôn`tsō), town, Friuli–Venezia Giulia, NE Italy, on the Isonzo River, near the Slovenian border. It is an agricultural center. The town was founded (late 15th cent.) by Venice as a fortress against the Turks. From 1754 to 1918 it formed with Gorizia (Görz) the crown land of Görz-Gradisca in the Austrian province of Küstenland.