The foibe are bulblike fissures in the ground that widen out to form a cave below. They are a common geological feature in Istria, Dalmatia, and the province of Trieste. During and immediately after World War II, these caves were used as dumping places for the thousands of Italians killed by Yugoslav partisans in a policy of deliberate ethnic cleansing in May–June 1945. Josip Brod Tito, the Yugoslav leader, was determined to eliminate resistance from the Italian community of Istria and to terrify Italian speakers into silence or flight. The bodies of the victims were thrown into the foibe to hide the extent of the massacre. The true numbers of Italians killed will never be known, but the likeliest figure (much contested by revisionists) is around 10,000. Tens of thousands of Italians fled Istria at the same time. For many years, the need to maintain good relations with the Yugoslav government led to the subject of the foibe being taboo, especially on the left, but the collapse of Yugoslavia and the subsequent civil war have reopened the subject. It should also be added that the brutal behavior of Italian troops in Croatia and Slovenia during the early part of the war had aroused the deep animosity of the local Slav population.
Historical Dictionary of Modern Italy. Mark F. Gilbert & K. Robert Nilsson. 2007.