Commercial vessels and ship building

Merchant vessels decreased in size in Late Antiquity, becoming much smaller than ancient Greek and Roman ones, although there are mentions in written sources of large capacity ships carrying wheat to Constantinople. Reductions in ship size and the lack of substantial funds for building new vessels led to the construction of flexible commercial ships, capable of transporting large quantities of cargo without losing speed or manoeuvrability when facing rough seas or pirates.

In addition to written texts, a valuable source of information on commercial vessels are shipwreck investigations, particularly the Yassi Ada shipwreck off Ancient Halicarnassus, opposite Kos, which has been dated to the early 7^th century on the basis of coins found on it, and the Serçe Liman shipwreck on the peninsula opposite Symi, which dates to around 1025. Yassi Ada was a trading ship about 20 metres long and 5.3 metres wide, with a cargo capacity of around 60 tons. This wreck is extremely interesting as regards the ship building techniques employed. Throughout Greco-Roman antiquity, ships were built according to the "planking first" principle, which meant that the hull was completed before the frame was fitted. The stem- and sternposts were first placed on the keel, and then covered in a shell of bonded strips of planking, which were planed and tightly joined in order to ensure a perfect fit and seal. The mast was raised after launching. In contrast, during the Middle Ages the frames of the ship were made first, according to the “frame first” principle, followed by a shell of planking that often needed caulking with tar. The shipwreck in Yassi Ada was constructed using the old technique up to the waterline, with the newer technique being followed for the rest of the ship. This places the ship at an intermediate stage in shipbuilding evolution. The Serçe Liman ship was constructed ​​entirely according to the second technique.

Another significant change was the invention of the single rudder, which steered the boat much more easily than the one or two large oars previously used near the stern. This change must have taken place ​​before the 10th century, both in Western Europe and in the Arab controlled Red Sea area. The widespread use of triangular sails went hand in hand with the building of even lighter commercial vessels called lateens. By the 12th century lateens were well established in the Mediterranean, and from there they spread to northern Europe. These changes enabled ships to make best use of the wind, rendered rowers almost unnecessary and allowed longer voyages. Finally, illustrations of ships found in Byzantine works of the Palaeologan period indicate that the shipbuilding was highly influenced by the Italians.

As far as navigation is concerned, we know that there must have been specialized sailors who calculated distances from points on land or based on the position of the sun and stars, using the astrolabe. Information on ports, coastlines, markets and the products of each region were contained in special books called periplous (circumnavigations); the only ones that have survived are the journey around the Red Sea (in the 3^rd century) and that around the Black Sea, which does not predate the first half of the 6^th century. The existence of maps with set courses and annotated reefs, shallows and distances between ports remains a matter of conjecture, as the oldest known portolan charts are from the 16^th century.

Warships and warfare 
Warships in Late Antiquity followed the shipbuilding tradition of the Greco-Roman world. The few surviving written sources mention small, manoeuvrable ships called triremes and liburnians, with a row of fifteen rowers on each side.

In the 6th century the dromons (“runners”) made their appearance. According to the historian Procopius , these took their name from the speed that they could reach. Dromons were the main Byzantine warships in the 10^th century. They were 40 metres long, with two banks of oars and one or two masts: a central one with a rectangular sail and a secondary one bearing a triangular sail, which was used for fast sailing when not giving battle. They were the largest ships in the fleet and had a crew of up to three hundred men. Those manning the bottom bank of oars were regarded as true oarsmen, whereas those above were more likely marines. The captain’s cabin (kravvatos) was located in the stern; from there, protected from the enemy arrows, he had a full picture of how events were unfolding. Shields were fixed at particular points on the ship’s side to protect the marines. The dromons had a raised corridor with war machines such as catapults, crossbows and cranes for firing projectiles at enemy ships during battle. At the base of the main mast there was an enclosed wooden tower called the xylokastron, from which soldiers could hurl stones, iron rods and clay vessels full of lime, snakes, lizards and scorpions at the enemy. A catapult for launching containers of Greek fire was mounted in the prow. The dromonia were auxiliary ships shaped like the dromons, with one or two masts with triangular sails; they were not armed as they were used for reconnaissance and special missions. The ram on the front of ships fell into disuse from the mid-7th century, only to reappear after the 14^th century, when warships were equipped with cannon. Other small boats were the chelandia, with two banks of oars and one or two masts with triangular sails for greater speed. They were divided into "ousiaka chelandia" with a crew of one hundred and ten men and "Pamphilus chelandia" with crews of up to one hundred and eighty men.

According to Naumachika (Naval Battles) by Leo the Wise , Byzantine naval tactics mainly relied on considering evidence that could be used to forecast the weather, so as to engage enemy ships under suitable conditions. The main concern of both the admiral and the ships’ commanders was to protect the crew and ships from storms. Battle formation depended on circumstances – a straight line was used to attack head on, but otherwise ships formed a semicircle, with the admiral’s dromon in the centre and the larger ships at the edges, to avoid being encircled by the enemy. When the signal to attack was given, each ship would speed up to draw close to the enemy fleet, having a particular vessel in its sights. On approaching the soldiers would try to break down the enemy defences, while the captain would give orders to draw up alongside the enemy ship and tie up to it, to enable the soldiers to board and begin fighting man to man.

Neorion, the military port at Constantinople, was in use for as long as the Byzantine Empire existed. After the 7th or 8th century the fleets of themes had local naval bases and shipyards for building new ships and repairing old ones. During the 10^th and 11^th century the “royal ploimon” still had a shipyard in Constantinople under the command of an exartistis. Small shipyards must also have existed in regional ports.