KALATCH, a town of Russia, in the country of the Don Cossacks, on the left bank of the Don above the confluence of the Karpovka, in 48° 43' N. lat. and 43° 30' E. long. Previous to the opening of the railway to Tsaritsin on the Volga, it was a place of only 500 inhabitants, but since that date (1862) it has increased to more than 12,000 inhabitants; and its transit trade has received a great development.