The territory of present-day Hungary has for centuries been a crossroads for various peoples, including Celts, Romans, Germanic tribes, Huns, West Slavs and the Avars. The foundations of the Hungarian state were established in the late ninth century AD with the conquest of the Carpathian Basin by Hungarian grand prince Árpád. His great-grandson Stephen I ascended the throne in 1000, converting his realm to a Christian kingdom. By the 12th century, Hungary became a regional power, reaching its cultural and political height in the 15th century. Following the Battle of Mohács in 1526, it was partially occupied by the Ottoman Empire (1541–1699). Hungary came under Habsburg rule at the turn of the 18th century, later joining with the Austrian Empire to form Austria-Hungary, a major power into the early 20th century.