His grandson Radbot, Count of Habsburg founded the Habsburg Castle, after which the Habsburgs are named. The origins of the castle's name, located in what is now the Swiss canton of Aargau, are uncertain. There is disagreement on whether the name is derived from the High German "Habichtsburg" (hawk castle), or from the Middle High German word "hab/hap" meaning "ford", as there is a river with a ford nearby. The first documented use of the name by the dynasty itself has been traced to the year 1108. The Habsburg Castle was the family seat in the 11th, 12th and 13th centuries. The Habsburgs expanded their influence through arranged marriages and by gaining political privileges, especially countship rights in Zürichgau, Aargau and Thurgau. In the 13th century, the house aimed its marriage policy at families in Upper Alsace and Swabia. They were also able to gain high positions in the church hierarchy for their members. Territorially, they often profited from the extinction of other noble families such as the House of Kyburg. By the second half of the 13th century, count Rudolph IV (1218–1291) had become one of the most influential territorial lords in the area between the Vosges Mountains and Lake Constance. Due to these impressive preconditions, on 1 October 1273, Rudolph was chosen as the King of the Romans and received the name Rudolph I of Germany. In a crucial step towards the creation of his own power base in the Eastern Alps, Rudolph led a coalition against king Ottokar II of Bohemia who had taken advantage of the Great Interregnum in order to expand southwards, taking over first the Babenberg (Austria, Styria, Savinja), and then the Spanheim inheritance (Carinthia and Carniola). In 1278, Ottokar was defeated and killed in the Battle of Marchfeld. The lands he had acquired in the previous decades were reverted to the German crown. In 1282, the Habsburgs gained for themselves the rulership of the duchies of Austria and Styria, which they then held for over 600 years, until 1918. The southern portions of Ottokar's former realm, Carinthia, Carniola, and Savinja, were granted to Rudolph's allies from the House of Gorizia. The resulting arrangement, known as the "Habsburg-Gorizia equilibrium in the Eastern Alps" lasted for half a decade.