The castles built in Hamburg from the 9th to the 11th centuries were dedicated as fortifications, e.g. Hammaburg, Bischofsturm, Domburg, Alsterburg and Neue Burg. All these castles are assumed to be located in the Altstadt quarter. Although only for the Bischofsturm (Bishop's tower) remains were found under the St Petri Church. Even later buildings were often fortifications, but from the 18th century wealthy citizens built their mansions or houses as country estates in the former outskirts, like Senator Martin Johann Jenisch in then independent Othmarschen.