Tessarakonteres, or simply "forty", was a very large catamaran galley reportedly built in the Hellenistic period by Ptolemy IV Philopator of Egypt. It was described by a number of ancient sources, including a lost work by Callixenus of Rhodes and surviving texts by Athenaeus and Plutarch. According to these descriptions, supported by modern research by Lionel Casson, the enormous size of the vessel made it impractical and it was built only as a prestige vessel, rather than an effective warship. The name "forty" refers not to the number of oars, but to the number of rowers on each column of oars that propelled it, and at the size described it would have been the largest ship constructed in antiquity, and probably the largest human-powered vessel ever built.

A galley was a type of ship which relied mostly on oars for propulsion that was used for warfare, trade, and piracy mostly in the seas surrounding Europe. It developed in the Mediterranean world during antiquity and continued to exist in various forms until the early 19th century. It typically had a long, slender hull, shallow draft, and often a low freeboard. Most types of galleys also had sails that could be used in favourable winds, but they relied primarily on oars to move independently of winds and currents. The term "galley" originated from a Greek term for a small type of galley and came in use in English from about 1300. It has occasionally been used for unrelated vessels with similar military functions as galley but which were not Mediterranean in origin, such as medieval Scandinavian longships, 16th-century Acehnese ghalis and 18th-century North American gunboats.