SOZOPOL, BULGARIA—Underwater archaeologists have spotted dozens of Roman, Byzantine, and Ottoman shipwrecks in the Black Sea off the coast of Bulgaria, Newsweek reports. The Black Sea Maritime Project (MAP), a two-year investigation of Bulgaria's Black Sea coast, seeks to document shipbuilding and port activity in the waters dating back 2,500 years. Since beginning the project in 2015, researchers have ventured as deep as 5,900 feet and have benefited from the unique composition of the Black Sea. The lower levels of the sea are anoxic, meaning that they do not contain oxygen and therefore provide an ideal environment for preserving wood, metal, and other materials that are damaged in oxygenated water. In addition to remaining uniquely well preserved, according to the team, the diverse range of styles of the vessels they have found attests to Bulgaria's location as a geographic and cultural crossroads throughout the centuries. To read more about the archaeology of shipwrecks, go to “History's 10 Greatest Wrecks.”