On a pedantic note, the Roman ship was not a galley, though it was often described as such.

“The Roman boat found in 1910 during the excavations for the concrete raft on which County Hall is built, excited much interest. Parts of the timbers were destroyed before their presence was recognized, but what was left of the boat was carefully lifted, treated with preservative and deposited in the London Museum. At the time she was thought to have been a Roman galley, and from the evidence of three coins found in her was dated at about the year A.D. 300. One theory was that she went down in a fight between Allectus and Constantius in the year A.D. 296, and the large round stone embedded in her timbers, which might have been ammunition thrown from a Roman ballista, lent colour to this assumption. (fn. 145)

More recently experts in nautical research have considered that her timbers were too lightly jointed for a sea-going vessel and that it was unlikely that she ever possessed a mast. It seems probable that she was a ferry boat plying across the river and that she became derelict in her old age or was sunk by accident. There was a large hole in her bottom and she may have met her end by drifting on to her mooring post in a high tide. This type of vessel would have been much shallower in draft than a galley and much shorter in proportion to her width. She could have been propelled by one man rowing her standing as is still done on vessels of this type. If, as is suggested on p. I, a Roman road from Canterbury crossed the river to Westminster from a point between Westminster and Lambeth Bridges, then this may have been one of the boats employed at the crossing; this is, however, conjecture. Her timbers had been repaired in a number of places, showing that she was an old boat when she met her end. A varied collection of pottery and other objects were found in and around her, most of which have been preserved.” http://www.british-history.ac.uk/survey-london/vol23/pp62-65

You left the best ’til last!

thanks