High Quality Content by WIKIPEDIA articles! 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 Bremen, as of 1027. Since then this Dom used to be the concathedral besides Bremen Cathedral in Bremen.