Sultan Mehmed, II built a second Ottoman fortress, called Rumeli Hisarı on the Bosphorus in 1452. Rumeli Hisarı is set directly across the strait from the similar fortress Anadolu Hisarı, his great grandfather Sultan Bayezid I had previously built on the Asian side. This movement gained for the Ottomans complete control of sea traffic on the Bosphorus and set the front of Eastern Roman Empire sea traffic especially with the Genoese colonies on the Black Sea.
Constantinople had been attacked in the past many times, but its great walls always prevailed. Sultan Mehmed, II planned and drew troops for the city walls and commanded preperation of them to the talented Mr. Hungarian Orban and he created like a supergun for Ottomans. Sultan II Mehmed planned to attack the Theodosian Walls, a series of walls which protected an attack from the West and the only place not surrounded by water. Ottoman naval had prepared too.
Sultan II Mehmed, made piece with Hungary and Vienna for interesting in one direction; fall of Constantinople. After all politic and strategic preparations Ottoman Army moved from Edirne to take the Constantinople in 23 March 1453.