"After a day of shopping, tell me what you saw?" You asked Wu Shun while spreading out a piece of paper on the table, dipping your pen in ink and starting to draw something.

Wu Shun said: "I saw a lot of restaurants, wine shops, tea houses, silk villages, fan shops, blacksmith shops... The streets were full of people, and there were many blue-eyed bearded bearded people, and there were many temples, chapels, ......., and the navel of the orchid was exposed outside the skirt......"

You say, "That's all?" ”

Wu Shun said, "Yes." That's what everybody sees. ”

You don't speak. When you're done drawing a piece of paper, you move it to Wu Shun's side and start drawing a second one.

Say, "Don't look through the eyes of a woman or a child." You have to look through the eyes of a soldier. As a soldier, in the troubled times, no matter which city you walk into, the only thing you should look at is its city defense deployment and city defects. ”

You motioned for Wu Shun to look at what you had just drawn. Wu Shun only glanced down, and he couldn't help sweating all over his body, feeling deeply ashamed. What you have drawn is a detailed schematic map of the city near Desheng Gate.

You draw them one by one. In a short time, 16 were drawn. Together, the city defense arrangement of the 16 city gates of the city is fully visible and clear at a glance. Wu Shun opened his mouth when he saw it, and his two eyes were about to be together.

The last one is a map of the north gate, on which you marked and drew the north gate and walls in detail. You change the color of paint, and at the junction of the walls and gates of the north gate, you draw a horizontal line. As can be seen from the diagram, this junction line is concave downward at the city gate, below the horizontal line. The recess runs through both sides of the city gate.

You say, "Put these away when the ink is dry, and take them back." This one at the north gate is installed, and when I meet him the day after tomorrow, I will take it to the Wuying Palace. ”

Wu Shun looked at the dense and detailed annotations on the map and said, "God! That's what you remember when you went shopping today? How is it possible to remember so much? ”

You say, "You remember a lot of messy things, but they are all useless in the war." ”

Wu Shun said: "What does this colored line represent? ”

You say, "On behalf of the horizon." You all passed through the north gate when you entered the city, did you notice anything out of the ordinary? ”

Wu Shun scratched his head and said, "Unusual? No, I don't. ”

You say, "It's ground." The ground is not normal. The floor tiles of the corridor under the city gate are not horizontal as a whole, but the middle part is seriously concave, and the whole corridor has become an upside-down turtle back shape, low in the middle and high on both sides. After leaving the city gate, about half a mile away, the road becomes horizontal, and after another half a mile, the road becomes the same as the ground of the city street, which becomes a turtle's back, high in the center and low on both sides. This is the normal design, when it rains, the street will drain smoothly and will not be prone to waterlogging. The corridor near the gate must have been of the same design before, but now it is seriously dented. ”

"Is it because there are so many people and horses in the middle?"

You shake your head. You say, "I was skeptical at first, but today we went to see the whole central street, and the other gates, and the gates of the royal city, and the roads are characterized by dense traffic and traffic, but all the ground is not so sunken." This can only show that there is a hole in the ground near the North City Gate that was not there before, and the ground is no longer solid. And how did this void come about? ”

You start drawing a new diagram. As you draw, you say, "The ground begins to sink before entering the city and ends half a mile after entering the gate." The degree of depression before entering the city is greater than that after entering the city. This shows that this invisible hole in the ground was first emptied from the moat. What is the underground structure of the moat? We walked a full circle along the moat today. The moat is so deep, where does the water come from, it can only be diverted from the underground river closest to the city, and the underground river is diverted into the moat ditch on the surface. How did this underground river go? Follow the wells of the whole city and you will know the route. All the wells in the north of the city are supposed to be drawn from underground rivers. However, the amount of water drawn is the largest near the North City Gate. Because we see it today, there are many paper mills, washing and dyeing workshops, and many flower gardens. There are many large wells in this area. ”

Wu Shun said: "What does this have to do with depressions? ”

"There is too much water on the ground in this area, which causes the groundwater to be over-pumped in this bend section, and the water level of the underground river is constantly decreasing, which drives the continuous subsidence of the ground above the river," you said. Over time, a cavity has formed in the ground. The hollow is getting bigger and bigger, and it is getting closer and closer to the ground, so as long as you concentrate manpower and dig down the city wall under the city gate for half an hour, it is estimated that you can dig the hole that connects to the underground. ”

"What's the use of digging into a hole?"

You say, "You can fill it with gunpowder, and once it is detonated, the entire North Gate and nearby fortifications will fly into the air." ”

You look straight at the map and say, "After the north gate was blown up, the besieging army poured in from here, and it was only such a short distance from the largest gate of the royal city. "You drew a connecting line on the map.

"After the huge underground explosion, the walls of this section of the royal city will be filled with cracks from top to bottom, if it will not partially crack and collapse." You say, "Do you understand now?" ”

Wu Shun said: "The dead hole in the city defense of Dongcheng is here!" ”

You say, "Yes." Because this dead hole was hidden underground, the city defense forces were unaware of its existence and did not notice its danger. The defenders of the castle only paid attention to the aspect of preventing a frontal assault on the city gates and storming the city walls, and ignored the possibility of making a city gate disappear completely. ”

Wu Shun looked at you and said, "Are you going to capture the city in the future?" ”

You say, "Are you so bold that you are not afraid that someone will accuse me of rebellion when they hear about it?" Wu Shun immediately stuck out his tongue and made a chilling gesture.

Say, "But all the cities will fall." It only depends on who and when. ”