With the demise of the Seljuk Sultanate of Rum during 12th to 13th century, Anatolia was divided into a patchwork of independent states, the so-called Anatolian Beyliks. For the next few centuries, these Beyliks were under the sovereignty of Mongolians and their Iranian Kingdom Ilkhanids. This accounts for the Persian nature of the later Ottomans. By 1300, a weakened Byzantine Empire had lost most of its Anatolian provinces to these Turkish principalities. One of the beyliks was led by Osman I (d. 1323/4), from which the name Ottoman is derived, son of Ertuğrul, around Eskişehir in western Anatolia. In the foundation myth expressed in the story known as "Osman's Dream", the young Osman was inspired to conquest by a prescient vision of empire (according to his dream, the empire is a big tree whose roots spread through three continents and whose branches cover the sky). According to his dream the tree, which was Osman's Empire, issued four rivers from its roots, the Tigris, the Euphrates, the Nile and the Danube. Additionally, the tree shaded four mountain ranges, the Caucasus, the Taurus, the Atlas and the Balkan ranges. During his reign as Sultan, Osman I extended the frontiers of Turkish settlement toward the edge of the Byzantine Empire.