Coffer (fortification)

Imagine you are building a castle to protect yourself from bad guys who want to hurt you. You build really tall walls and use big heavy stones so the bad guys can't get in.

But then you realize that the walls can't be too thin or else they will break easily. So you come up with an idea to make the walls stronger. You make a special layer inside the walls called a coffer.

A coffer is like a special frame made of wood or stone that you put inside the walls. It helps to make the walls thicker and stronger. It also makes it harder for bad guys to break through the walls because they have to get through the extra layer first.

So now your castle is really safe because you have thick walls with a coffer inside. And the bad guys can't get through!