which became free ports, competed with Venice more and more economically. Habsburg Trieste in particular boomed and increasingly served trade via the Suez Canal, which opened in 1869, between Asia and Central Europe, while Venice very quickly lost its competitive edge and commercial strength. During the Second World War, the historic city was largely free from attack, the only aggressive effort of note being Operation Bowler, a successful Royal Air Force precision strike on the German naval operations in the city in March 1945. The targets were destroyed with virtually no architectural damage inflicted on the city itself. However, the industrial areas in Mestre and Marghera and the railway lines to Padua, Trieste, and Trento were repeatedly bombed. On 29 April 1945, a force of British and New Zealand troops of the British Eighth Army, under Lieutenant General Freyberg, liberated Venice, which had been a hotbed of anti-Mussolini Italian partisan activity. Geography Venice sits atop alluvial silt washed into the sea by the rivers flowing eastward from the alps across the Veneto plain, with the silt being stretched into long banks, or lidi, by the action of the current flowing around the head of the Adriatic Sea from east to west. Subsidence Subsidence, the gradual lowering of the surface of Venice, has contributed—along with other factors—to the seasonal Acqua alta ("high water") when much of the city's surface is occasionally covered at high tide. Building foundations Those fleeing barbarian invasions who found refuge on the sandy islands of Torcello, Iesolo, and Malamocco, in this coastal lagoon, learned to build by driving closely spaced piles consisting of the trunks of alder trees, a wood noted for its water resistance, into the mud and sand, until they reached a much harder layer of compressed clay. Building foundations rested on plates of Istrian limestone placed on top of the piles. Flooding Between autumn and early spring, the city is often threatened by flood tides pushing in from the Adriatic. Six hundred years ago, Venetians protected themselves from land-based attacks by diverting all the major rivers flowing into the lagoon and thus preventing sediment from filling the area around the city. This created an ever-deeper lagoon environment. Additionally, the lowest part of Venice, St. Mark's Basilica, is only above sea level, and one of the most flood-prone parts of the city. In 1604, to defray the cost of flood relief, Venice introduced what could