The Black Sea Maritime Archaeology project says it found the wreck off the Bulgarian coast at a depth of 2 kilometers (1.2 miles) in oxygen-free conditions that preserved its components. The group says the vessel has been carbon dated to more than 2,400 years ago.
The project has spent three years surveying the area using technology previously available largely to oil companies. It discovered some 60 shipwrecks, including a 17th century Cossack raiding fleet and Roman trading vessels carrying amphorae.
A documentary on the project will open Tuesday at the British Museum.