The population of Rome reached nearly a million during its Imperial period, when Roman commerce dominated the Mediterranean. Large merchant ships and warships were constructed to move goods and protect the fleet and homeland, respectively. Roman ships contained basic structural parts that were duplicated on most of their vessels.
Hulls and Keels
The length of Roman merchant and commercial ships varied extensively, but they were usually 100 to 180 feet long and had beam widths of 20 feet or so. The keels were made of pine and fir, including several mortis joints to join the keel into one large structural component. Merchant ship hulls generally had deeper profiles that steadied them in rough seas. Warship hulls and keels were constructed similarly, except for thicker side hulls, sometimes reinforced with lead plate. Roman warships averaged between 100 and 120 feet, with beams around 18 feet.
The Corvus on Roman ships served as a movable gangplank that could be dropped over the side rails of another ship for boarding. The wide Corvus facilitated the boarding of enemy vessels for the purpose of attacking the deck crew. The Corvus could be released and secured to another vessel in minutes. A smaller, narrower Corvus was used on commercial and merchant ships.
Many Roman warships had a tower on the bow or stern. This permitted archers to fire down on soldiers and deckhands on an opposing vessel. The towers could also hold catapults that hurled stones and burning pitch at the enemy. The height of the towers allowed clearance for the archers to fire above the heads of their shipmates. Merchant ships did not need or carry this type of defensive platform, since it added unnecessary weight and made the ship top-heavy.
Ramming beaks on Roman warships were bronze, reinforced projections that connected to the bow. They sat at or slightly below the waterline and were used to pierce an enemy vessel's side hull planks. The speed and impact was generated by the oarsmen, who had to row as fast as possible to ensure a solid breach. Merchant vessels had no such ramming beaks, possessing only a curved figurehead on the bow.
Sails and Rigging
Merchant ships and warships had tall main masts with rectangular sails typically made of white linen, papyrus or byssus. Due to its flax content, byssus was the most expensive and exotic sail. Smaller square sails were often rigged to the stern and bow. A triangular sail, called a supparum, was later added to assist in upwind sailing. Rigging lines consisted of finely woven hemp.
The rudder system consisted of a single long oar hung over the stern quarter, or a double-oar set-up on vessels over 150 feet in length. A cable system attached to a main tiller allowed both oars to be turned simultaneously. The system of levers and cables enabled the helmsman to control the vessel in strong currents and rough weather.
Roman warships typically had one or two rowing decks situated below the main deck and above the bilge area. Some of the largest galleons had three rowing decks that were staggered in elevation to cut down on height. Standing platforms or benches were provided for the oarsmen. It took anywhere from 50 to 80 men to propel a Roman warship. Most early merchant ships had no oar decks at all, since the space below the main deck was reserved for cargo.
Roman merchant ships and warships featured spacious cabins. The high castle on the stern was a large, boxlike cabin area that housed the captain, high-ranking officers and steersmen. The forecastle deck room, mounted on the bow end of the main deck, carried the soldiers and deck crew. Merchant ships also had these accommodations, with the high castle reserved for the most important crew and the captain, while the forecastle housed traders, passengers and some of the lowliest crew members.