The most interesting sightseeing location of Bad Mergentheim is the castle of Deutschordenschloss. The knights of Teutonic order used the castle of Deutschordenschloss as their home base. The Deutschordenschloss castle is a complex of buildings that were build over the period of 800 years. Some of the buildings were built in 12th century, and later on the castle was expanded. Teutonic Knights were members of the order of Brothers of the German House of Saint Mary in Jerusalem. It was a military order, and the knights served during the crusading military campaigns in the Middle Ages.