The siege of Plevna or Pleven, was a major battle of the Russo-Turkish War of 1877–1878, fought by the joint army of the Russian Empire and the Kingdom of Romania against the Ottoman Empire. After the Russian army crossed the Danube at Svishtov, it began advancing towards the centre of modern Bulgaria, with the aim of crossing the Balkan Mountains to Constantinople, avoiding the fortified Turkish fortresses on the Black Sea coast. The Ottoman army led by Osman Pasha, returning from Serbia after a conflict with that country, was massed in the fortified city of Pleven, a city surrounded by numerous redoubts, located at an important road intersection.