It is impossible to say with certainty how far inland that control extended.[13] Süleyman further ceded "all the castles that the emperor had possessed in Turkey". The return of some fortresses on the coasts of Anatolia is confirmed by the Byzantine historian Laonikos Chalkokondyles, but no details are known from Byzantine sources.[14][15] The identity of at least some of these castles is provided by the Ottoman historian Ashikpashazade, who reports that c. 1419, Sultan Mehmed I recovered the forts of Hereke, Old Gebze, Darıca, Pendik and Kartal, on the northern shore of the Gulf of Nicomedia, which had been in Byzantine hands until then.