An Qingxu
In January 757 AD, An Lushan was killed by his own son An Qingxu. In the same month, An Qingxu ordered general Yin Ziqi () to besiege Suiyang. Yin Ziqi joined with Yang Chaozong before the siege, with a total army size over 130,000 men. The governor of Suiyang at the time, Xu Yuan (), heard of Zhang Xun's fortress defence abilities in the Battle of Yongqiu and asked him for help. Zhang Xun knew that if Suiyang fell, the rest of Tang's territory south of the Yangtze River would be threatened. He agreed to help immediately.