In 750, discontent in the caliphate had reached a critical level due to the treatment of non-Arab citizens in the Empire. The Abbasid Revolution resulted in the overthrow of the Umayyad Caliphate, ushering in the Abbasid period. Several settlements, including Murwab, were developed during the Abbasid period. Over 100 stone-built houses, two mosques, and an Abbasid fort were constructed in Murwab during this era. Murwab fort is the oldest intact fort in the country and was built over the ruins of a previous fort which was destroyed by fire. The town was the site of the first sizable settlement established off the coastal area of Qatar. A similar site, containing T'ang stoneware and dating to the 9th and 10th centuries, was discovered in Al Naman (north of Zubarah). Substantial development in the pearling industry around the Qatari Peninsula occurred during the Abbasid era. Ships from Basra en route to India and China would make stops in the port of Qatar during this period. Chinese porcelain, West African coins and pieces from Thailand have been discovered in Qatar. Archaeological remains from the 9th century suggest that Qatar's inhabitants used greater wealth, perhaps from pearl trade, to construct higher quality homes and public buildings. However, when the caliphate's prosperity declined in Iraq, so too did it in Qatar. Most of Eastern Arabia, particularly Bahrain and the Qatari Peninsula, were sites of revolt against the Abbasid Caliphate around 868. Mohammed ibn Ali, a revolutionary, roused the people of Bahrain and Qatar into a rebellion, but the rebellion was unsuccessful and he relocated to Basra. He was later successful in instigating the Zanj Rebellion. A radical Isma'ili group called the Qarmatians established a utopian republic in Eastern Arabia in 899. They considered the pilgrimage to Mecca a superstition and once in control of the Bahraini state they launched raids along the pilgrim routes crossing the Arabian Peninsula. In 906 they ambushed the pilgrim caravan returning from Mecca and massacred 20,000 pilgrims. Qatar is mentioned in 13th-century Muslim scholar Yaqut al-Hamawi's book, "Mu'jam Al-Buldan (Dictionary of Countries)", which alludes to the Qataris' fine striped woven cloaks and their skills in improvement and finishing of spears, known as khattiyah spears. The spears acquired their name as an homage to the region of Al-Khatt which encompassed present-day Qatif, Uqair and Qatar.