Artificial preservation prevented the lake from evolving into a marshland. The Su Causeway built by Su Shi, and the Bai Causeway built by Bai Juyi, a Tang dynasty poet who was once the governor of Hangzhou, were both built out of mud dredged from the lake bottom. The lake is surrounded by hills on the northern and western sides. The Baochu Pagoda sits on the Baoshi Hill to the north of the lake. Arab merchants lived in Hangzhou during the Song dynasty, due to the fact that the oceangoing trade passages took precedence over land trade during this time. There were also Arabic inscriptions from the 13th century and 14th century. During the later period of the Yuan dynasty, Muslims were persecuted through the banning of their traditions, and they participated in revolts against the Mongols. The Fenghuangshi mosque was constructed by an Egyptian trader who moved to Hangzhou. According to Odoric of Pordenone, Hangzhou was the greatest city in the world. It was heavily populated and filled with large family estates. It had twelve thousand bridges. Bread, pork, rice, and wine were abundant despite the large population. Ibn Battuta is known to have visited the city of Hangzhou in 1345; he noted its charm and described how the city sat on a beautiful lake and was surrounded by gentle green hills. During his stay at Hangzhou, he was particularly impressed by the large number of well-crafted and well-painted Chinese wooden ships with colored sails and silk awnings in the canals. He attended a banquet held by Qurtai, the Yuan Mongol administrator of the city, who according to Ibn Battuta, was fond of the skills of local Chinese conjurers. Hangzhou was chosen as the new capital of the Southern Song dynasty in 1132, when most of northern China had been conquered by the Jurchens in the Jin–Song wars. The surviving imperial family had retreated south from its original capital in Kaifeng after it was captured by the Jurchens in the Jingkang Incident of 1127. Emperor Gaozong moved to Nanjing, then to modern Shangqiu, then to Yangzhou in 1128, and finally to Hangzhou in 1129. The Song government intended it to be a temporary capital, but over the decades Hangzhou grew into a major commercial and cultural center of the Song dynasty, rising from being a middling city of no special importance to being one of the world's largest and most prosperous.