One of the first battles of the First World War. Some two weeks after their declaration of war, the Austrians launched their invasion of Serbia on 12 August, crossing the River Jadar to the west of Belgrade, where the Serbs had expected the attack to fall. The Austrians had 200,000 men against a slightly smaller and badly equipped, but experienced Serbian force. The Serbs launched their counter attack on 16 August, and after a few days fighting the Austrians were forced back across the river.