]Second biggest harbor built on the coast of Marmara Sea, the Harbor of Theodosius (Portus Theodosiacus) was established by Theodosius I (379-395) in Area XII on the bay which had a big indentation. Existing harbor’s capacity was insufficient, so it became compulsory to build new harbors or enlarge the existing ones. The deep natural bay that sits at the entrance of Lykos Creek was possibly enlarged in the period of Emperor Theodosius and a breakwater which stretches out from west to east was built on the south side in order to satisfy the needs of the time. The existence of granaries like horrea Alexandrina (Granary of Alexandria) in the east end of Area IX of the Theodosius Harbor and horrea Theodosiana which has the emperor’s name, indicates that it is a big commercial harbor which ships from Alexandria and other places unload grain and other materials. It is known that grain trade continued until the occupation of Egypt in 641 by Arabs. Previosuly, grain was transported directly to the city. Transportation with big tonnage open-sea ships used to be interrupted while crossing the Dardanelles because of wind and current, because of these reasons ships had to wait in front of the bosphorus. Therefore it is known that granaries was built in Tenedos (Bozcaada) by order of İustinianos and after this point cargo was transported with small ships. Additionally supplying the city with brick, tile, lumber and provisions and Marble from Prokonnesos (Marmara Adası) which is used in construction activities, shows that the harbor was in a lively structure.
Today, it is known that in the base of the wall of the Langa there was a town overflowing the south walls of Marmara located between Mustafa Kemal and Namık Kemal streets which steep down from Aksaray to the Marmara coast and it was inhabited by Jewish people starting from 13th century. Although the Theodosius Harbor significantly lost its function in mid 7th century with the end of the grain trade from Egypt, it was still used as a harbor which was proven by the shipwrecks found in the excavations and dating back to 7th-11th century. In this period it was mostly used as a harbor to take shelter in by short distance cargo ships and fishing boats. As a result of alluvium soil carried by Lykos (Bayrampaşa) Creek, the harbor was abandoned after 12th century and from that day on it became the place of piling debris. Petrus Gyllius who visited the city in 16th century mentions about the harbor filling: “Harbor is filled, greenery is planted on the broad vegetable gardens, very few arbor (tree) is planted.”