Hello there little one! So, have you ever heard of Mithraism? It's a really old religion that people used to follow a long time ago.
So, imagine a long time ago, people believed in lots of different gods and goddesses. But the people who followed Mithraism, they believed in just one god, named Mithras.
They believed that Mithras was a god of light, and that he could protect them from evil. They would have these big gatherings and special ceremonies called "Mithraic Mysteries".
One of the most important things about Mithraism was that it had something called "grades". That meant that you started at a lower level and worked your way up to be more important in the religion.
People who were part of Mithraism also believed that they needed to be good people in order to be accepted by Mithras. That meant they had to follow certain rules and be kind and helpful to others.
So, in short, Mithraism was an ancient religion that believed in one god named Mithras, and it had special ceremonies and rules to follow to make sure people lived good lives.