The "prima nave" is the one which conforms most closely to the naval architecture of the Roman imperial period. It is 70 metres long with a beam of 20 metres and a round bilge. A curving prow with the arc turning inward to the centre of the ship at its tip and a stern in the form of fish's tail. In plan view it forms a regular elipse while the "second ship" is more like a massive pontoon, square in plan view. The first ship is, therefore, most representative of the general characteristics which come to mind when thinking of the classical roman ships as reproduced in pictures, mosaics and sculpture.