Bochum (; Westphalian: Baukem) is a city in the state of North Rhine-Westphalia, Germany and part of the Arnsberg region. It is located in the Ruhr area and is surrounded by the cities (in clockwise direction) of Herne, Castrop-Rauxel, Dortmund, Witten, Hattingen, Essen and Gelsenkirchen. With a population of nearly 365,000, it is the 16th most populous city in Germany.