Okay kiddo, so a loooong time ago, in a place called the Byzantine Empire, there were these things called "districts." Think of them like big neighborhoods with their own special rules. One of these districts was called kleisoura.
Now, kleisoura was a little different from other districts because it was actually a fortified military zone. That means it was a place where soldiers lived and worked to protect the empire from bad guys who wanted to do it harm.
But even though it was a military zone, people still lived there too! Families and regular folks would live alongside the soldiers and help support them.
So, think of kleisoura like a big, guarded neighborhood where brave soldiers worked hard to keep everyone safe!