A stone wall is like a big puzzle made of rocks. You know how you like to play with blocks and fit them together to make something cool? Well, people did the same thing with rocks a long time ago to make walls.
They would find big rocks that were the same size and shape, and then they would stack them on top of each other. But sometimes the rocks didn't fit perfectly, so they had to use smaller rocks to fill in the gaps.
The walls were really strong, so they could keep people and animals inside a place or keep enemies out. Plus, they looked pretty cool too! Even today, some people still make stone walls to decorate their gardens or to mark their property.