Berezina (byĕrāzēnäˈ) [key], river, c.380 mi (610 km) long, rising in Belarus. It flows generally S past Borisov and Bobruysk into the Dnieper River. It is navigable for most of its length. The heroic retreat across the Berezina of the remnants of Napoleon's Grand Army took place near Borisov from Nov. 26 to Nov. 29, 1812. The crossing—effected under heavy Russian attack—saved Napoleon and his forces from capture, but lost the lives of more than 20,000 men.