An Qingxu, now emperor of Yan, orders his general Yin Ziqi to besiege Suiyang (in modern day Shangqiu, Henan).

Yin Ziqi joins with Yang Chaozong before the siege, with a total army size over one hundred and thirty thousand men.

The governor of Suiyang, Xu Yuan, had heard of Zhang Xun's fortress defense abilities in the Battle of Yongqiu and asks him for help.

Zhang Xun knows that if Suiyang falls, the rest of Tang's territory south of the Yangtze River will be threatened.

He agrees to help immediately.

The united army of Zhang Xun and Xu Yuan, around seven thousand men, prepares to defend Suiyang with their lives.

Xu Yuan focuses on supplies management and after-battle repairs.

Zhang Xun, on the other hand, focuses on battle tactics.

The Tang soldiers never let up despite daily sieges by the Yan army.

Zhang Xun's troops play the war-drums during the night, acting as if they are going to fight (a tactic that army apparently had used before).

Consequently, the Yan army is forced to stand on guard during the night, and suffers from the lack of sleep.

Eventually, some troops do not bother to put on their armor when they hear these battle drums, and continue sleeping.

After the Yan army lowers their defenses, Zhang Xun's forces ambush them very successfully.

Zhang Xun has long wanted to give the Yan morale a major blow, and the best way to do this is to hurt or kill the Yan general Yin Ziqi.

Zhang orders his troops to shoot weeds, instead of arrows, at a few enemy soldiers.

When these soldiers notice that they are being shot by weeds, they are overjoyed, and promptly run to Yin Ziqi to report that the Tang army has already run out of arrows.

Zhang Xun notices where the soldiers run and orders his best archers to shoot at Yin Ziqi.

One such arrow hits Yin Ziqi in his left eye, throwing the Yan army instantly into chaos.

The siege ends with this expected major blow to the Yan morale.

After sixteen days of siege and ambush, Yan has already lost twenty thousand men.

Yin Ziqi decides that his army is too tired to fight, so he orders a temporary retreat to regroup.

Yin Ziqi returns to besiege Suiyang two months later, with an additional twenty thousand fresh troops.

Xu Yuan had prepared for the upcoming battle by storing a year’s worth of food inside Suiyang fortress, but the district governor had insisted that he share the large food supply with other nearby fortresses.

Hence, the food supply has become much less than what Xu Yuan had originally planned.

The Tang soldiers, having fallen into a serious food shortage by July, receive very small daily rations of rice.

If they want more food, they must settle for whatever animals, insects, and tree roots can be found in their vicinity.

Yin Ziqi, noticing the famine plaguing the Tang army, orders more troops to surround Suiyang.

He makes many siege attempts with siege ladders, but they are all repelled by the determined Tang troops.

Yin Ziqi even uses hooked pulled carts, to try to pull down the towers of the fortress, with limited success.

The Tang soldiers are able to destroy the hook of these carts, before major damage is made, but even with the battle success, Zhang Xun knows that with only around sixteen hundred soldiers left, and most of them sick or hungry, the battle must soon be lost.

All of the insects, animals and vegetation in the besieged area of Suiyang have been eaten by August.

Zhang Xun orders thirty of his best soldiers, including his best soldier captain Nan Jiyun, to break though and seek help from nearby fortresses.

Nan Jiyun and twenty-six others successfully beak through; however, none of the nearby local governors are willing to offer troops and food supplies.

Finally, Nan Zhu Yun asks for help from Helan Jinming, governor of the nearby Linhuai.

Helan has long been jealous of Zhang Xun's abilities.

He also wants to preserve his forces, so he refuses to assist Zhang Xun.

He instead, hoffers Nan Jiyun a large feast in an attempt to persuade him to join his ranks.

Nan replies, "The reason why I risked my life to come here is because the local civilians and my comrades have no food to eat for over a month. How can I eat such a huge feast when I know that my comrades are facing? Although I failed my mission, I will leave a finger with you, as evidence that I did come here."

Immediately after, Nan Jiyun cuts off (or, in some versions, bit off) one of his own fingers.

He then rides away.

Nan Jiyun’s bravery finally convinces a local governor Lian Huan to lend him three thousand soldiers.

Both of them fight their way though the Yan ranks back into Suiyang.

Fighting though the numerous Yan army is damaging, and only about a thousand of the soldiers from the outside make it inside the fortress.

The starving Tang soldiers, numbering about sixteen hundred in total and with no chance of outside help, fall into despair.

Almost everyone tries to persuade Zhang Xun to surrender, or find some way of escape south.

Besieged Suiyang had long been in a state of famine by September.

The Old Book of Tang says: Yin Ziqi had besieged the city for a long time.

The food in the city had run out.

The dwellers traded their children to eat and cooked bodies of the dead.

Fears were spread and worse situations were expected.

At this time, Zhang Xun took his concubine out and killed her in front of his soldiers in order to feed them.

He said, "You have been working hard at protecting this city for the country wholeheartedly.

Your loyalty is uncompromised despite the long-lasting hunger.

Since I can't cut out my own flesh to feed you, how can I keep this woman and just ignore the dangerous situation?"

All the soldiers cried, and they did not want to eat.

Zhang Xun ordered them to eat the flesh.

Afterwards, they caught the women in the city.

After the women were run out, they turned to old and young males.

20,000 to 30,000 people were eaten.

People always remained loyal.

Xu Yuan also killed his servants to feed the soldiers, which was recorded in The New Book of Tang: An explanation for the people remaining loyal is explained in The New Book of Tang: After the city was besieged for a long time, at the beginning, the horses were eaten.

After horses ran out, they turned to the women, the old, and the young.

30,000 people in total were eaten.

People knew their death was close, and nobody rebelled.

When the city fell, only 400 people were left.

It is possible that all dead soldiers and civilians were also eaten after this incident.

The Tang soldiers defending Suiyang fight bravely until early October.

Finally, with fewer than four hundred men alive, and the men without the strength to shoot arrows, Suiyang falls to the Yan army.

Although Yan has won this series of battles, the losses have ben enormous.

Before the Battles of Yongqiu and Suiyang, Yan had intended to conquer all of the Tang Dynasty.

Their total army size, across the whole country, was well over three hundred thousand men, greatly outnumbering what the Tang army could have offered at the time.

After these two battles, however, the tide turns and the Tang army now holds the upper hand in both manpower and equipment.

If Yan had conquered the entire Suiyang district even one year earlier, the Tang Dynasty might have ended in 757.

The Suiyang campaign marks the turning point of the war.