Saint Mary's Cathedral in Hamburg (German: Sankt Mariendom, also Mariendom, or simply Dom or Domkirche, or Hamburger Dom) was the cathedral of the ancient Roman Catholic Archdiocese of Hamburg (not to be confused with Hamburg's modern Archdiocese, est. 1994), which was merged in personal union with the Diocese of Bremen in 847, and later in real union to form the Archdiocese of Hamburg-Bremen, as of 1027.
In 1180 the cathedral compound turned into the cathedral close (German: Domfreiheit; i.e. cathedral immunity district), forming an exclave of the Prince-Archbishopric of Bremen within the city of Hamburg. By the Reformation the concathedral was converted into a Lutheran church. The cathedral immunity district, since 1648 an exclave of the Duchy of Bremen, was seized by Hamburg in 1803. The city then prompted the demolition of the proto-cathedral between 1804 and 1807.