2009 L'Aquila earthquake region saw dozens of significant aftershocks following the main earthquake. The strongest, which hit at 19:47 CEST on 7 April, measured magnitude 5.3 and caused further damage. According to the Italian National Geophysics Institute director Boschi, the aftershock epicentres migrated south-east, thus lessening the risk of further major shocks near populated areas. Aftershocks caused safety problems for rescue crews searching for injured victims trapped in precarious structures in the historic center of L'Aquila, a medieval city. Using cranes and backhoes to remove loose bricks and broken timbers, the crews were aware that even a small aftershock could have triggered the
Italian city-states town revolts led to the foundation of city-states throughout medieval Europe, such as in Russia (Novgorod Republic, 12th century), in Flanders (Battle of Golden Spurs, 14th century) in Switzerland (the towns of the Old Swiss Confederacy, 14th century), in Germany (the Hanseatic League, 14th–15th century), and in Prussia (Thirteen Years' War, 15th century). Some Italian city-states became great military powers very early on. Venice and Genoa acquired vast naval empires in the Mediterranean and Black Seas, some of which threatened those of the growing Ottoman Empire. During the Fourth Crusade (1204), Venice conquered a quarter of the Byzantine Empire. The