Mazarrón is a municipality in the autonomous community and province of Murcia, southeastern Spain. The municipality has an area of 318.7 square kilometres (123.1 sq mi), and a population (2008) of more than 34,351 inhabitants. A military fort (named C1 or Castillitos-small castles) built between 1930 and 1936 during the reign of Alfonso XIII of Spain and the Second Spanish Republic exists as a tourist attraction on the old road between Mazarrón and Cartagena, and although it is accessible from the Bay of Mazarrón it is not in the municipality itself.