High Quality Content by WIKIPEDIA articles! Four battles 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 troopers repulsed an attack against the peak by the Ottoman Central army.