Rome in the Footsteps of an XVIIIth Century Traveller

The Bosphorus, now called, The canal, is, according to the antients, fifteen miles long; (..) The narrowest part is thought to be between Rumelli Hissari (The castle of Romelia), and Anatole Hissari (The Eastern or Asiatic castle and consequently it must have been there, at the temple of Mercury on the Europe side, that Darius built a bridge, in order to lead his army against the Scythians. The castle on the Asia side was built by Bajazet the first, when he besieged Constantinople about three hundred and fifty years ago.
Richard Pococke - A Description of the East and Some Other Countries - 1745
Anadolu Hisar was built by Sultan Bayezit I (1389-1402) to move his troops from Anatolia to Europe safely. In particular the fortress was built to support the siege of Constantinople enforced by the Sultan in 1396. The other purpose of the fortress was to block supplies to the city from the remaining Byzantine possessions in the Black Sea and in particular from Trebizond.

View from the Bosporus

Byzantines and Ottomans were not the only players on the Bosporus. Two other powers had strong interests in controlling the waterway: Venice and Genoa. It was a sort of strategy game where each player pursued his own advantage and changes of alliances were very frequent with one remarkable exception: Venice and Genoa would never stay on the same side.
Genoa had a strong economic influence in the region with a well organized trade route on the Black Sea. Relations between Genoa and the Ottomans were generally good and in 1354 the Ottomans established their permanent rule over a series of towns on the European coast of the Sea of Marmara thanks to an alliance with Genoa. For this reason the Genoese did not react to the construction of Anadolu Hisar.

Walls near the harbour

The main purpose of the fortress was to protect a small bay where a few Ottoman ships could moor and to provide a secure location for the sultan's troops while they were waiting to be ferried across the Bosporus. A small stream near the fortress provided a supply of fresh water.

Outer walls and towers, also in the image used as background for this page

The fortress was composed of an inner square castle surrounded by walls strengthened by a few towers. At that time artillery had not yet been developed, so Anadolu Hisar was designed to cope with catapults and similar siege engines.

Ottoman miniature showing (left) Rumeli Hisar and (right) Anadolu Hisar

The threat posed by Anadolu Hisar to the passage of hostile ships was rather limited, even when towards 1450 new weaponry (cannon and bombards) was introduced. The fortress was built on a bay and the Bosporus was at that point large enough for ships to sail along the European side without great risk of being hit.
Sultan Mehmet II realized that to effectively block supplies to Constantinople he needed a stronger fortress on the other side of the Bosporus: Rumeli Hisar (the rock of Europe).

"A Cemetery by the Bosporus" by Warwick Goble, a 1906 illustration of "Constantinople", a Black's Beautiful Book (see a page with other works by Goble portraying people and street scenes)

Fortresses of the Sultans - Introduction
Fortresses built before 1453:
1 - Anadolu Hisar
2 - Rumeli Hisar
Fortresses built after 1453 and before 1657:
3 - Kale Sultanieh
4 - Kilitbahir
Fortresses built after 1657:
5 - Seddulbahir
6 - Imbro
7 - Tenedo