The Provinces of Prussia constituted the main administrative divisions of Prussia. Following the dissolution of the Holy Roman Empire in 1806 and the Congress of Vienna in 1815 the various princely states in Germany gained their nominal sovereignty, but the reunification process that culminated in the creation of the German Empire in 1871, produced a country that was constituted of several princely states and dominated by one of them, the Kingdom of Prussia. The Provinces of Prussia covered some 60 percent of the territory that was the German Empire. The appointed head of each province was known as Oberpräsident. Each province also had a provincial diet (Provinziallandtag in German). The provinces of Prussia were further subdivided into Regierungsbezirke.