Lake Baikal was known as the "North Sea" in historical Chinese texts. It was situated in the then Xiongnu territory that stretched from the empire of the Han Dynasty in the south, to the Siberian taiga north of the lake, and saw military excursions led by the army of the Han Dynasty engaging the Xiongnu during the Han-Hun Wars. Little was known to Europeans about the lake until Russia expanded into the area in the 17th century. The first Russian explorer to reach Lake Baikal was Kurbat Ivanov in 1643.
The Trans-Siberian railway was built between 1896 and 1902. Construction of the scenic railway around the southwestern end of Lake Baikal required 200 bridges and 33 tunnels. Until its completion, a train ferry transported rail cars across the lake from Port Baikal to Mysovaya for a number of years. At times during winter freezes, the lake could be crossed on foot—though at risk of frostbite and deadly hypothermia from the cold wind moving unobstructed across flat expanses of ice. A mass-crossing of military-historical significance, which did indeed leave many dead from cold-exposure was the 1920 Great Siberian Ice March. Beginning in 1956, the impounding of the Irkutsk Dam on the Angara River raised the level of the lake by 1.4 m (4.6 ft).
As the railway was built, a large hydro-geographical expedition headed by F.K. Drizhenko produced the first detailed contour map of the lake bed.
Lake Baikal is in a rift valley, created by the Baikal Rift Zone, where the Earth's crust pulls apart.At 636 km (395 mi) long and 79 km (49 mi) wide, Lake Baikal has the largest surface area of any freshwater lake in Asia, at 31,722 km2 (12,248 sq mi), and is the deepest lake in the world at 1,642 m (5,387 ft). The bottom of the lake is 1,186.5 m (3,893 ft) below sea level, but below this lies some 7 km (4.3 mi) of sediment, placing the rift floor some 8–11 km (5.0–6.8 mi) below the surface: the deepest continental rift on Earth. In geological terms, the rift is young