As Arthur watched, the defenders who boarded the mobile fortresses were quickly routed and defeated by the invaders. There were crushed and killed. Then the mobile fortresses resumed firing on the wall.

But things didn't end there. The invaders sent their troops to the underground passage in order to counterattack. They wanted to take advantage of the method that the defenders used to catch them off guard.

Their elite troops flooded the tunnels. These were foundation establishment cultivators with the power of golden core cultivators due to their armored suits and there were 10 of them sent from each mobile fortress.

So there were 500 effective golden core soldiers sent to counterattack. This was far more than the combined number of golden core cultivators of the five sects. If these 500 golden core cultivators manage to reach the wall, one can easily imagine what will happen.

In response to this, the tunnels were quickly destroyed and collapsed. This managed to trap some of the invaders, but it didn't kill them because of the protection of their armored suits.

In fact, the collapsed tunnels couldn't trap them for long. They were too strong to be trapped by some earth. So they would dig themselves out soon.

In the meantime, the overall situation of the battlefield had returned to what it was before the defenders sent troops to board the mobile fortresses. Both sides returned to throwing attacks at each other from a safe distance.

This remained a bad situation for the defenders because they still couldn't withstand the barrage of the mobile fortresses. The wall was essentially a rank 4 artifact. The only reason it could withstand the firepower of rank 5 war machines was that it had the support of the walls behind it.

The more walls there are, the stronger the individual walls would be. This was because the walls were built based on a formation that Sword Flash had designed.

Right now, there are 11 walls, so each wall is 10 times stronger than it should be. But this is not going to be enough to make the first wall withstand the constant firepower from rank 5 mobile fortresses indefinitely.

The first wall was going to be destroyed soon. But the patriarchs, who had given the order to use the rank 5 bombs earlier, refused to do anything to stop it.

Instead of doing something to prevent the destruction of the first wall and the weakening of the overall fortification arrangement, they asked the defenders to withdraw from the first wall.

They also asked builders and formation masters like Arthur to begin the construction of buttress walls whose sole purpose is to support the main walls.

The buttress walls are small and short. This made it possible for them to be built between two main walls.

They can't withstand artillery fire at all. They were built quickly for the sole purpose of making up for the loss of a wall. So a lot of corners were cut in their structural integrity.

It was clear that the patriarchs were giving up in the first wall. This surprised Arthur, but it didn't delay him from following orders. He quickly went to work enchanting the new buttress walls.

The invaders quickly demolished the first wall. But this put them out of range of the second wall. If they are to attack the second wall, they would have to move closer to it. This meant that they would have to go through the minefield, moats, and traps that had been laid on the battlefield.

If they could fly, these minefields wouldn't be a problem. But flying was prohibited, so they had to brave the danger.

They had no choice but to wade into the minefields. As they did, they discovered that the explosives and traps buried in the ground weren't much of a problem. This was because the mines and traps were too weak to damage their mobile fortresses. The only problem that they would have to figure out was how to get past the moat filled with poisonous acid liquid.

Since they couldn't fly, getting through the lake of poisonous acid was going to be a problem for them. But when they thought that this was all that they had to deal with, the ground collapsed beneath them.

Apparently, there were a lot of empty spaces underground, and all the explosions that went off earlier weren't just to damage the invaders as they crossed the battlefield. They learned about this too late.

The ground sank and trapped them, creating holes that were more than 100 meters deep. Then the acid in the moat flowed into the caverns in the ground, trapping them.

The acid was only effective at rank 4. So it shouldn't have damaged the fortresses too much. Unfortunately for the invaders, some of their fortresses had holes in their hulls.

The holes in their hulls were blown open by the bombs earlier. The people who were sent to board the mobile fortresses have all died, so they basically failed to accomplish their mission. But the acid flood rushing into the mobile fortresses quickly finished what they had started.

The first row of mobile fortresses was the ones trapped in the caverns. They were 10 in number. So out of the total 55 mobile fortresses, 10 of them had been put out of commission, even if only temporarily.

The mobile fortresses were not destroyed by the acid flood. They could still be repaired and made to run. Most of the damage was done to the personnel and soldiers on the mobile fortresses.

However, the elite troops with the armor suit at the fourth mortal coil, and their leaders with the armor suit as the fifth mortal coil, managed to survive the flooding of the acid. This was because their armor suits protected them.

The armor suits were meant to protect them in worlds with unfavorable and inhospitable environmental conditions. So some acid flood can't kill them, no matter how poisonous it is. They were able to rush out of the acid-soaked mobile fortresses.