 In spring 759, the Yan general Shi Siming, who had briefly submitted to Emperor Suzong but then turned against Tang again, attacked Tang forces at Yecheng and caused them to collapse and scatter, and then killed An Qingxu, taking over as Yan's emperor.He then attacked south.With Guo blamed for the collapse at Yecheng, Li Guangbi was put in overall command of Tang forces in the region, and he put Xu in charge of defending Bian Prefecture (汴州, in modern Kaifeng, Henan).