It's called The Apotheosis of War by Vasily Vereschagin, a Russian painter of the late 19this century. Here's the description the Tretyakov Gallery site gives it, "The viewer beholds a dead wasteland baked by the sun with stunted trees. In the distance there is a plundered city. In the centre, a pyramid of human skulls. Such were the “monuments” which the 14th-15th century conqueror Tamerlane (Timur) left after himself. Originally the artist intended to name the painting The Triumph of Tamerlane, however he preferred to give it a larger scale significance and wrote on the frame The Apotheosis of War, adding “This is dedicated to all great conquerors, past, present and future.”"