 Frederick, one of the seven Prince-electors, was a member of the House of Wettin, which since 1089 had ruled over the adjacent Margravate of Meissen up the Elbe river - established under Emperor Otto I in 965 - and also over the Landgravate of Thuringia since 1242.Thus, in 1423, Saxe-Wittenberg, the Margravate of Meissen and Thuringia were united under one ruler, and as a unified territory gradually became known as, "Upper Saxony".When Elector Frederick II died in 1464, his two surviving sons overrode the "primogeniture principle" and divided his territories by the Treaty of Leipzig on 26 August 1485.