Humans have long known the defensive effects of the city walls. From ancient to modern times, I do n’t know how many offensive and defensive battles have been staged. When the Mongols began to conquer the world, the nomadic cavalry regiments who were good at the field were helpless against siege. I quickly mastered the siege tactics and integrated the siege weapons from various places to achieve a good effect. Many sturdy towns were destroyed. Those thin walls in Europe at that time could not resist the Mongolians at all. Attacks, especially by the Mongols, began to use a variety of powerful firearms, which were even more destructive. Since then, due to the improved firepower of artillery, the role of city walls has gradually disappeared from human history. The text is intended to explain:. ['How the Mongolian Corps conquered Europe.', 'How the city wall exited the stage of history.', 'How the firearms played a role in the siege.', 'How the Mongolian Nomadic Regiment adjusted its tactics.']