Tylos Fortress lies on the nort east corner of the tell of Qal'at al-Bahrain in the village of Al Qalah in Bahrain.
The site of the tell has been inhabited by man since 2300 BC and was the site of the capital of the ancient Dilmun civilization.
Exactly when Tylos Fortress was built is unknown. The fortress is never mentioned in texts and all that is known is a result of archeological finds. Most probably it was built during the reign of the Sasanid king Ardashir I over Bahrain, at that time named Tylos, to protect navigation of the Persian Gulf, from Arab Bedouins and pirates. Ardashir ruled from 226 to 241 AD. The Sasanids dominated the eastern coast of Arabia and administered it through Arab vasal tribes from their homeland in present-day Iran. The fortress was used as a military-administrative complex in a harbour town. After the 7th century the town and fortress seem to have lost their importance and the site declined to probably nothing more than a small fishing village.
During the 13th century the site regained its importance and the old Tylos fortress was converted into a commercial warehouse by the Salgharid Atabaks of Fars, during the Mongol dynasty of the Il-Khans. The harbour traded with China and India and 8 date presses, called madbasa or mudabissa, were installed in the fort which yearly could produce 15.000 kg of date honey.
Between the late 13th century and the early 14th century the Mongol rulers lost their power and the Arab-Persian dynasty of the Princes of Hormuz took control of the Strait of Hormuz and the prinicipal harbours of the Persian Gulf region. This resulted in the building of a new fort directly south west of the Tylos fortress, which was to become Bahrain Fort. After that Tylos Fortress seems to have disappeared.
The fort was discovered during archeological excavations in the 2nd half of the 20th century.
It was built as a coastal fortress with a square ground plan of 55 by 55 meters encompassed by a moat. It had round towers at its corners and in the middle of its north, east and south side. There was a gate at its west side, fortified by 2 towers.
Tylos Fortress is freely accessible but, as it is an archeological site, you are supposed to stay out of the remains of the fortress itself. This must have been a nice fort. It is a nice bonus when you visit Bahrain Fort. The Bahrain Fort Museum, next to the beach, is also worth your visit.