In 1423, Margrave Frederick IV was assigned the heirless Duchy of Saxe-Wittenberg, formerly held by the House of Ascania, by Emperor Sigismund in turn for his support against the Hussites. The Wettin rulers thereby entered into the Saxon electorate, in which they ultimately merged their margravial lands abandoning Meissen's status as an independent principality; though they retained the margravial title. In the late 15th century, the dynasty held a large contiguous territory between the Werra and Oder rivers. By the 1485 Treaty of Leipzig, however, the Upper Saxon lands were again divided between Frederick's grandsons Ernest ruling in Wittenberg and Albert, who took the former Meissen territory. The treaty marked the beginning of the permanent separation of the two states of Saxony and Ernestine Thuringia.