Rumelihisarı is situated at the narrowest point with 660 meters of the Bosphorus strait, just opposite of Anadoluhisarı (Anatolian Castle) on the Anatolian side, which is another Ottoman fortress that was built between 1393 and 1394 by Sultan Bayezid I.

Rumelihisarı was built by Sultan Mehmed II between 1451 and 1452 in order to control the sea traffic on the Bosphorus strait and prevent aid from the Black Sea to reach Constantinople during the Turkish siege of the city in 1453, particularly from the Genoese colonies such as Caffa, Sinop and Amasra. In a previous Ottoman attempt to conquer the city, Sultan Murad II (1404–1451) had encountered difficulties due to a blockade of the Bosphorus by the Byzantine fleet. The necessity of a fortress opposite of Anadoluhisarı was thus well known to the Ottomans. On the location of Rumelihisarı, there had been a Roman fortification in the past, which was used as a prison by the Byzantines and Genoese. Later on, a monastery was built there.

In preparation for the conquest of Constantinople, Sultan Mehmed II (1432–1481), son of Murad II, started to realize the construction of the fortress immediately following his second ascent to the throne in 1451. He refused the plea for peace of the Byzantine Emperor Constantine XI (1404–1453), who understood the intention of the Sultan. The construction began on 15 April 1452. Each one of the three main towers was named after the Pashas who supervised their construction. The Sultan personally inspected the activities on the site. With the help of thousands of masons and workers, the fortress was completed in a record time of 4 months and 16 days on 31 August 1452.

The sultan wanted to cheer up the builders so he allegedly ordered them to build the castle in the shape of the name of Muhammad the Muslim prophet, which can be seen from above. Muhammad and Mehmed share the same Arabic spelling , and so he may have also made the fortress as an homage to himself.

Construction of the Rumeli Castle

The legend has it, Mahmut Pasha, the Grand Vizier, tells to Sultan Mehmet Khan “Your Excellency, from now on we should start to work for taking the Konstantiniyye”.

The army directed to Konstantiniyye stays waiting at Eskihisar near Kocaeli city. The sultan sends a delegate to the Emperor Constantinus. The delegate tells the Emperor that the Conqueror went there to rest and to enjoy the fine air and water and he would be a neighbor for several days. And he stayed there for couple of months.

One day Mahmut Pasha says the Conqueror “Your Excellency, if we don’t do a castle on the opposite coast, you cannot take Konstantiniye”. And he took a piece of cattle leather and says “let’s ask for a land as small as this leather”. They sent a delegate for conveying their demand to Constatinus. Constantinus accepted the Conqueror’s demand. Then the Conqueror chopped up the cattle leather and turned it into a long rope. Then he surrounded a field with this rope and had the Rumeli Castle built in there. When Constantinus learned it, he regretted. But his regret did not change the situation.