Isonzo(ēzôn`tsō), river, 87 mi (140 km) long, rising in the Julian Alps, NW Slovenia, and flowing S through Slovenia, where it is known as the Soča, then SW through NE Italy before emptying into the Gulf of Trieste. At the entrance to the Venetian plain, the Isonzo valley was the scene of many battles during World Wars I and II. After World War II, the part of the valley above Gorizia, Italy, was given to the former Yugoslavia.
(in Slovene, Soča), a river in Yugoslavia and Italy. Length, 136 km; basin area, about 3,500 sq km. Rises in the Julian Alps in Yugoslavia. It crosses the Italian-Yugoslav border near Gorizia, flows out onto the Friulian Plain, and empties into the Gulf of Trieste in the Adriatic. The river is fed by snow and rain. High water is in the spring and autumn; low water is in the summer and winter. The average water discharge is 135 m3/sec. There are several hydroelectric power plants along the Isonzo. In its lower course the river is navigable.
During World War I (1914–18) there were fierce battles on the Isonzo between the Italian and Austrian and German forces (1915–17). The river was the site of the so-called 11 battles on the Isonzo, in which the Italians failed to penetrate the enemy’s defenses.