German Bohemians, later known as Sudeten Germans, are ethnic Germans living in the Czech lands of the Bohemian Crown, which later became an integral part of Czechoslovakia. Before 1945, over three million German Bohemians constituted about 23% of the population of the whole country and about 29.5% of the population of Bohemia and Moravia. Ethnic Germans migrated into the Kingdom of Bohemia, an electoral territory of the Holy Roman Empire, from the 11th century, mostly in the border region which was later called the Sudetenland, named after the Sudeten Mountains.