By the first half of the 1st century AD, steering gear mounted on the stern were also quite common in Roman river and harbour craft as proved from reliefs and archaeological finds (Zwammderdam, Woerden 7). A tomb plaque of Hadrianic age shows a harbour tug boat in Ostia with a long stern-mounted oar for better leverage. The boat already featured a spritsail, adding to the mobility of the harbour vessel. Further attested Roman uses of stern-mounted steering oars includes barges under tow, transport ships for wine casks, and diverse other ship types. Also, the well-known Zwammerdam find, a large river barge at the mouth of the Rhine, featured a large steering gear mounted on the stern. According to new research, the advanced Nemi ships, the palace barges of emperor Caligula (37-41 AD), may have featured 14 m long rudders.