A (war?) ship from Ostia. Compare to this merchant ship and this small boat.
"For the first contest enter four well-matched ships of heavy oars, picked from all the fleet. Mnestheus with his eager crew drives the swift Sea Dragon, soon to be Mnestheus of Italy, from whose name comes the Memmian line; Gyas the huge Chimaera of huge bulk, a city afloat, driven forward by the Dardan youth in triple tier, with oars rising in threefold rank. Sergestus, from whom the Sergian house has its name, rides in the great Centaur; and in the sea-blue Scylla Cloanthus, whence comes your family, Cluentius of Rome!"
Virgilius - the Aenaid V 114
Translated by Fairclough, H. R.