A powerful German princely family whose roots can be traced back to the 11th century. They took their name from a former Prussian province (now part of the state of Baden-Württemberg in Germany). From 1415 they ruled the electorate of Brandenburg and the following century saw great expansion, Margrave Albert becoming grand master of the Teutonic Knights in 1511. In 1614 the duchy of Cleves was acquired and in 1701 the Elector Frederick III of Brandenburg took the title of Frederick I of Prussia. In 1871 William I of Prussia took the title Emperor William I of the German Empire. His grandson William II abdicated in 1918. A member of a second branch, Prince Charles Hohenzollern-Sigmaringen, was elected Prince of Romania in 1866, becoming King Carol in 1881. His brother Leopold was offered the throne of Spain in 1870 and turned it down, an incident that Bismarck used to provoke war with France by altering the Ems telegram.