The Battle of Shipka Pass consisted of four battles that were fought between the Russian Empire, aided by Bulgarian volunteers known as Opalchentsi, and the Ottoman Empire for control over the vital Shipka Pass during the Russo-Turkish War (1877–1878). The crucial moment came in August 1877, when a group of 5,000 Bulgarian and 2,500 Russian troops repulsed an attack against the peak by a nearly 40,000 strong Ottoman army.