Substantial development in the pearling industry around the Qatari Peninsula occurred during the Abbasid era. Ships voyaging from Basra to India and China would make stops in Qatar's ports during this period. Chinese porcelain, West African coins and artefacts from Thailand have been discovered in Qatar. Archaeological remains from the 9th century suggest that Qatar's inhabitants used greater wealth to construct higher quality homes and public buildings. Over 100 stone-built houses, two mosques, and an Abbasid fort were constructed in Murwab during this period. When the caliphate's prosperity declined in Iraq, so too did it in Qatar. Qatar is mentioned in 13th-century Muslim scholar Yaqut al-Hamawi's book, "Mu'jam Al-Buldan", which alludes to the Qataris' fine striped woven cloaks and their skills in improvement and finishing of spears. Much of Eastern Arabia was controlled by the Usfurids in 1253, but control of the region was seized by the prince of Ormus in 1320. Qatar's pearls provided the kingdom with one of its main sources of income. In 1515, Manuel I of Portugal vassalised the Kingdom of Ormus. Portugal went on to seize a significant portion of Eastern Arabia in 1521. In 1550, the inhabitants of Al-Hasa voluntarily submitted to the rule of the Ottomans, preferring them to the Portuguese. Having retained a negligible military presence in the area, the Ottomans were expelled by the Bani Khalid tribe in 1670. In 1766, members of the Al Khalifa family of the Utub tribal confederation migrated from Kuwait to Zubarah in Qatar. By the time of their arrival, the Bani Khalid exercised weak authority over the peninsula, notwithstanding the fact that the largest village was ruled by their distant kin. In 1783, Qatar-based Bani Utbah clans and allied Arab tribes invaded and annexed Bahrain from the Persians. The Al Khalifa imposed their authority over Bahrain and retained their jurisdiction over Zubarah. Following his swearing in as crown prince of the Wahhabi in 1788, Saud ibn Abd al-Aziz moved to expand Wahhabi territory eastward towards the Persian Gulf and Qatar. After defeating the Bani Khalid in 1795, the Wahhabi were attacked on two fronts. The Ottomans and Egyptians assaulted the western front, while the Al Khalifa in Bahrain and the Omanis launched an attack against the eastern front. Upon being made aware of the Egyptian advance on the western frontier in 1811, the Wahhabi amir reduced his garrisons in Bahrain and Zubarah in order to redeploy his troops.