Bochum dates from the 9th century, when Charlemagne set up a royal court at the junction of two important trade routes. It was first officially mentioned in 1041 as "Cofbuokheim" in a document of the archbishops of Cologne. In 1321, Count Engelbert II von der Marck granted Bochum a town charter, but the town remained insignificant until the 19th century, when the coal mining and steel industries emerged in the Ruhr area, leading to the growth of the entire region. The population of Bochum increased from about 4,500 in 1850 to 100,000 in 1904. Bochum acquired city status, incorporating neighbouring towns and villages. Additional population gains came from immigration, primarily from Poland.