The attack method formulated by An Qingxu and Cui Qianyou was as follows: while feints were carried out in the direction of the east gate and the north gate with a scale of several thousand people, in the direction of the south gate, the attack team of 10,000 people continued to attack the head of Tongguan City.

While ordering the sergeants to cross the forbidden ditch and climb to the west edge to prepare to ascend the city, the sergeants of 10,000 people were ordered to carry stones and soil, as well as cut down trees and bamboos, to fill in the narrowest section of the forbidden ditch on the east side outside the south gate, preparing to fill in this forbidden ditch and turn it into a thoroughfare again.

An Qingxu's confidence in daring to make such a decision came from the 150,000 horses under his command, as well as the arrival of nearly 200,000 horses led by his father An Lushan, who was only a two-day trip. It is guessed from the situation found during the daytime attack that there are only more than 10,000 Tang troops in the city at most, and the combat effectiveness is not strong, if the city is attacked overnight, and the Tang army can not see clearly at the head of the city at night, it will provide them with a convenient opportunity to fill in the forbidden ditch, and fill in a section of the forbidden ditch while attacking the city. Then, after filling in the forbidden ditch for a while, and then increase the intensity of the attack, Tongguan City must be captured.

As soon as An Qingxu's order was given, the rebel attack also began. The first 10,000 horses descended from the east edge of the ditch to the ditch in a continuous manner, managed to climb to the west edge of the ditch, and then climbed the city with a ladder, and the sergeants who were responsible for filling the ditch also began to fill in the ditch with sacks, filling the ditch with dirt and stones, and using large sections of wood and bamboo.

However, after the attack began, An Qingxu and Cui Qianyou, who commanded the operation, discovered that the situation was abnormal.

The average distance between the east side of the forbidden ditch and the south gate of Tongguan is 80 steps, that is, about 120 meters, which is basically within the range of the Tang army's arrows on the beacon tower of the city head and the 12 cities.

Of course, the bed crossbows at the head of the city also began to shoot continuously.

After discovering that the rebels were preparing to attack the city overnight, the 8,000 men and horses led by Dou Hua and Zhang Yan, who had been given a short rest and food and drinking supplements, were also replenished to the south gate under Yang Xi's order. In this way, the defensive force in the direction of the south gate was nearly 16,000 people, which was double the original number of personnel, the number of sergeants fired in each wave was also doubled, and the number of arrows flying out of the city naturally doubled.

The number of sergeants on the beacon towers of the twelve cities has also increased to three hundred in each city!

"Report to the general, the arrows of the Tang army at the head of the city are very dense, and our army has suffered heavy casualties!" A sergeant ran to a lieutenant general who commanded the siege battle, and reported the situation in a panic, "The reinforcements of the Tang army seem to have arrived, and the city is full of people!"

"Got it, probe again!" This Zhonglang surnamed Wu frowned, and angrily ordered the sergeant who came to report to inquire about the situation again, and after the sergeant ran away, he immediately passed the sergeant on standby beside him, "Quickly report the attack to His Royal Highness the Crown Prince and Vice Marshal Cui, the reinforcements of the Tang army have arrived, the arrows on the city are more dense than during the day, and our army has suffered heavy losses!"

"Yes, General!" The sergeant on standby immediately ran away and reported the situation to An Qingxu and Cui Qianyou, who were watching the battle on the hill behind.

"What? Tang army reinforcements have arrived in Tongguan? After hearing the sergeant's report on the battle situation and the situation of the Tang army in the city, An Qingxu was taken aback.

In fact, just now he had already sensed something strange from the shouts of the Tang army at the head of the city and the unusual sound of war drums, and he was already guessing whether the follow-up Tang army had arrived at Tongguan, but he didn't expect to be really guessed by him.

"Did the Tang army reinforcements really arrive at Tongguan?" Cui Qianyou was also surprised.

Judging from the battle situation in the afternoon, the follow-up Tang army did not arrive at Tongguan, but the current situation seems to be different from the afternoon, the formation of the Tang army at the head of the city seems to have changed, the arrows shot down are more dense than during the day, and the shouts are louder.

But neither An Qingxu nor Cui Qianyou was sure if it was true that Tang army reinforcements had arrived.

They don't want this situation to happen, if it is really the follow-up brigade of the Tang Army to arrive at Tongguan, then there is no way to fight this battle, the forbidden ditch is dangerous, and all their men and horses will not be able to rush to the head of Tongguan City.

Because of doubts, An Qingxu did not give a new order, and the charge through the forbidden ditch and the filling of the earth continued.

Under the intensive arrow fire of the Tang army at the head of the city, a large number of charging sergeants fell on the edge of the forbidden ditch or in the forbidden ditch, and the sergeants who were about to transport mud to fill the ditch were also shot down on the east side of the forbidden ditch, and the soil they transported could not be filled in the ditch. For a time, the eastern edge of the forbidden ditch was littered with corpses, and countless wounded people lay there groaning and screaming in pain, hoping to get help from their companions, but in exchange for other things, they ignored them, and even trampled on them.

The number of rebel sergeants fired on the eastern edge of the forbidden ditch was so large that the sergeants who followed up were greatly disturbed.

There were also a lot of corpses and injured people who had rolled down the forbidden ditch, and the other large sections of the forbidden ditch that had been washed away began to fill the corpses again.

The average height of the city wall of Tongguan City is about four or five zhang, about thirteen or fourteen meters, plus the height difference of the terrain, it is at least seven or eight zhang higher than the east edge of the forbidden ditch and almost twenty meters, and the beacon towers of the twelve cities are more than one zhang higher than the city wall, and it is nearly ten zhang higher than the east edge of the forbidden ditch, and it is thirty or forty meters higher than the bottom of the forbidden ditch. Because of the impact against the height of the terrain, the rebels stood on the east edge of the forbidden ditch and fired a salvo, and it was possible to shoot on the city wall, but the strength was already weak, and it was difficult to shoot on the beacon tower of the Twelve Cities, unless it was a fierce general with great strength like Wang Sili and Pang Zhong.

The rebel sergeants who rushed to the bottom of the forbidden ditch could not even push the arrows so high, so it can be said that the rebels' charge had to brave the rain of arrows, and the casualties on both sides were completely disproportionate.

"Report to His Royal Highness the Crown Prince, the arrows of the Tang army are very dense, and more than two thousand people have been killed and wounded, but no one has rushed through the forbidden ditch!"

The sergeant's report again made An Qingxu feel even more uneasy, he was completely sure that the follow-up reinforcements of the Tang army had arrived in Tongguan, and he also knew that with the arrival of the reinforcements of the Tang army, the effect of their attack at night could no longer achieve expectations, and after thinking painfully for a while, An Qingxu made a decision that he couldn't figure out whether it was wise or stupid.

"Pass on the prince's order, the whole army stops attacking!"

The black light blinds, it is very difficult to go up and down the forbidden ditch, even if the light is sufficient during the day, you must be careful, otherwise it is easy to fall, and the difficulty increases exponentially at night. Reinforcements from the Tang army had arrived, and under the intense fire of arrows from the city, the soldiers carrying mud could not even rush to the edge of the forbidden ditch.

In such a situation, in order to avoid greater casualties, An Qingxu could only reluctantly issue an order to stop the attack, but changed to a small team of men and horses to continue to attack the city, and could only fight again after dawn!