The Battle of Ankara or Angora was fought on 20 July 1402 at the Çubuk plain near Ankara, between the forces of the Ottoman Sultan Bayezid I and the Emir of the Timurid Empire, Timur. The battle was a major victory for Timur, and it led to the Ottoman Interregnum. Timur, a Turco-Mongol from Transoxiana (now Uzbekistan), had built an empire in Central Asia over the years, and became the most powerful ruler in Central Asia since Genghis Khan. He sought to rebuild the once great Mongol Empire. In the 1380s and 1390s, he invaded and conquered parts of Persia (including Azerbaijan and Upper Mesopotamia), ravaged southern Russia and Ukraine (1395–96), and sacked Delhi (1398). Although there had been tensions between the Ottomans and Mongols, nothing would warrant a war, until Bayezid demanded tribute from an emir loyal to Timur, which he understood to be a personal affront and a reason for war. In 1400–01 Timur took Sivas from the Ottomans, parts of Syria from the Mamluks, and next directed towards Anatolia. Meanwhile, in 1402, the Ottomans had been campaigning in Europe. Bayezid broke off the blockade of Constantinople and marched to Ankara after Timur again moved his army to the southeast in the summer of 1402. It is estimated that the Timurid army counted 140,000, mostly cavalry, and also 32 war elephants. Bayezid's army numbered 85,000. Historical sources exaggerated the number of troops to unrealistic proportions: Ahmad ibn Arabshah claimed 800,000 Timurid troops, while a German witness claimed 1.6 million, for instance. The Ottoman force included contingents under his sons, Ghazis, Janissaries, Anatolian Muslim vassals, and various European (Balkan Christian) vassals. Among Serbian vassals participating were Stefan Lazarević, Vuk Lazarević, Đurađ Branković and his brother Grgur Branković, and among Albanian were Koja Zakarija, Demetrius Jonima, Gjon Kastrioti, and probably Tanush Dukagjini. Christian vassals that did not participate include Zetan Konstantin Balšić. A quarter of the Ottoman troops were recently conquered Tatars.