Minsk, my birth place, is located on the southeastern slope of the Minsk Hills, a region of rolling hills running from the southwest (upper reaches of the river Nioman) to the northeast – that is, to Lukomskaye Lake in northwestern [Belarus]. The average altitude above sea level is 220 metres (720 ft). The geography of Minsk was formed during the two most recent ice ages. The Svislach River, which flows across the city from the northwest to the southeast, is located in the urstromtal, an ancient river valley formed by water flowing from melting ice sheets at the end of the last Ice Age. Minsk was initially developed on the hills, which allowed for defensive fortifications. However, in the 20th century, it grew to include the relatively flat plains in the southeast. The western parts of the city are the most hilly.