Ok, kiddo! Do you know about the Mongols? They were a group of people who lived a long, long time ago and they were really good at fighting and conquering other places. They even made their own big empire!
But the people who lived in a place called Sichuan didn't want to be conquered by the Mongols. So they built special forts to protect themselves from the Mongols.
These forts were very cleverly designed. They had really tall walls and watchtowers where people could see if the Mongols were coming. The walls were made with different layers of materials like bricks and stone so that they would be stronger and harder to break down.
The forts also had special traps and obstacles around them. They had spikes hidden underneath the ground, so if the Mongols tried to run across them, they would get hurt. There were also big logs that could be rolled down the hills to crush anyone who was coming too close!
The people in Sichuan were very smart and worked very hard to build these forts. And because of them, they were able to keep the Mongols from taking over their land.