The immense, ruined Bahla Fort, with its walls and towers of mud brick on stone foundations and the adjacent Friday Mosque with its decoratively sculpted prayer niche (mihrab) dominate the surrounding mud brick settlement and palm grove. The fort and settlement, a mud-walled oasis in the Omani desert, owed its prosperity to the Banu Nebhan tribe (Nabahina), who dominated the central Omani region and made Bahla their capital from the 12th to the end of the 15th century. From there they established relationships with other tribal groups of the interior. Bahla was the centre of Ibadism (a branch of Islam), on which the ancient Omani Imamates were based and whose influence can be traced across Arabia, Africa and beyond. The extensive wall (sur) with sentry walk and watchtowers enclosing the labyrinth of mud brick dwellings and cultivatable land has several gateways. The oasis is watered by the falaj system of wells and underground channels bringing groundwater from distant springs, and by management of the seasonal flow of water. Bahla is an outstanding example of a fortified oasis settlement of the medieval Islamic period, exhibiting the water engineering skill of the early inhabitants for agricultural and domestic purposes. The pre-gunpowder style fort with rounded towers and castellated parapets, together with the perimeter sur of stone and mud brick technology demonstrates the status and influence of the ruling elite. The remaining mud brick family compounds of traditional vernacular houses (harats) including al-Aqr, al-Ghuzeili, al-Hawulya and the associated mosques, audience halls (sablas), bath houses, together with the dwellings of the fort guards (askari) demonstrate a distinctive settlement pattern related to the location of the falaj. The importance of the settlement is enhanced by the Friday mosque with its highly ornate mihrab and the remains of the old, semi-covered market (souq), comprising a complex of single-storey shops fronting onto narrow lanes, the whole enclosed by an outer wall. The location of the souq placed it within easy surveillance from the fort on its rocky outcrop nearby. Remains of carved and decoratively incised timber doors, shelves and window screens testify to a rich, thriving craft tradition. Criterion : The Bahla Fort and oasis settlement with its perimeter fortification are an outstanding example of a type of defensive architectural ensemble that enabled dominant tribes to achieve prosperity in Oman and the Arabian Peninsula during the late medieval period.