The historical riches of Istanbul are not limited to the land but also include cultural heritages underwater. The earthquakes, storms, rise of sea levels or sunken ships have enriched the cultural underwater heritage of Istanbul throughout the history.

Conducted by the Directorate of Istanbul Archaeological Museums between 2004 and 2013, the rescue excavations in the construction site of Yenikapi Marmaray and Subway Projects revealed the Port of Theodosius (Portus Theodosiacus) which was one of the biggest ports of Constantinople during the Byzantine Period. Following the 9^th century, the alluvial deposits carried by Lykos or today’s Bayrampasa Stream filled the Port of Theodosius in time. Thanks to this alluvial deposit that covered the port, 37 sunk ships and countless small artefacts were perfectly preserved. Revealed with the excavations, the submerged objects also qualify as the highest number of sea equipment from the Early Middle Ages that have been unearthed in an archaeological area.

The Vordonisi Island, one of the important diving places of Istanbul which is encountered in historical texts but was not discovered until recently, remained under the Marmara Sea due to a natural disaster. It is believed that the island remained under water in consequence of a major earthquake which occurred during the 1100s. Found at a spot between Dragos and Kucukyali 1km from the shore, the Monastery Rocks led to the Vordonisi Island with an underwater survey carried out in 2016.

These investigations held as part of the North Eastern Marmara underwater researches also documented the remnants of the exile monastery of Patriarch Phoitos with aerial photographs. The surface operations also identified a sunken ship bearing a Marmara Island marble and various scattered tiles underwater. The dating activities are still in progress.

During the underwater researches made by Beylikduzu Municipality throughout the 13km coast of the district, 8 artefacts were found submerged in water including breakwater, ancient port and ancient sunken objects. The researches shed light to the history of Istanbul by uncovering significant findings such as a 3,5km long harbour and a breakwater system.