 Because the land routes between the Song and Jin were controlled by the Liao , diplomatic exchanges had to occur by traveling across the <unk> Sea . Negotiations for an alliance began secretly under the <unk> that the Song wanted to acquire horses from the Khitans . Song diplomats traveled to the Jin court to meet Aguda in <unk> , while Jurchen envoys arrived in the Song capital Kaifeng the next year . At the beginning the two sides agreed to keep whatever Liao territory they would seize in combat . In 1120 , Aguda agreed to cede the Sixteen Prefectures to the Song in exchange for transfer to the Jin of the annual tributary payments that the Song had been giving the Liao . By the end of 1120 , however , the Jurchens had seized the Liao Supreme Capital , and offered the Song only parts of the Sixteen Prefectures . Among other things , the Jin would keep the Liao Western Capital of <unk> at the western end of the Sixteen Prefectures . The two sides agreed that the Jin would now attack the Liao Central Capital , whereas the Song would seize the Liao Southern Capital , Yanjing ( modern day Beijing ) . 
