Arid to semi-arid desert area, occupying a plateau and forming most of Botswana and extending into Namibia, Zimbabwe, and South Africa; area about 900,000 sq km/347,400 sq mi. The only permanent river, the Okavango, flows into a delta in the northwest, forming marshes that are rich in wildlife. The British explorer, David Livingstone, crossed the Kalahari in 1849.