So, imagine you have a big piece of paper that tells a story about a place called Upper Moesia. This story is written in a language that not everyone can understand, kind of like when grown-ups talk about things you don't know yet.
But some very smart people called archaeologists found these big pieces of paper and studied them a lot. They found out that they were actually written a long, long time ago by people who lived in Upper Moesia, which is now part of present-day Bulgaria and Serbia.
The paper had special marks called inscriptions, which were kind of like pictures but with a different meaning. The inscriptions were made by carving the story into big stones, so that people in the future could read about it too. Kind of like when you write your name on the sidewalk with chalk for everyone to see.
The inscriptions on these stones told us a lot about the people who lived in Upper Moesia a long time ago. They told us about their leaders, their gods, and even about the soldiers who protected them from bad guys.
Now these inscriptions are kept safe in museums, so that people can learn about the story of Upper Moesia and the people who lived there a long, long time ago.