The Beylik of Osman was formed in 1299 by Turkish mercenaries immigrating to central Anatolia, in the employ of many of the feudal muslim nations in Anatolia. By mid-1300, it had invaded the north of Byzantine holdings in Anatolia, taking a wide swathe of land that included Heraclea. However, Byzantine forces pushed back, and Osman forces retreated to their own territory, and agreed to a peace treaty. After that, dealings with the Byzantine Empire were very peaceful.