When we talk about a "monumental inscription," we are talking about writing that is put on a really big object or building. It's like when you draw a picture on a piece of paper, except it's written on something much bigger - like a statue or a tombstone.
These inscriptions are usually very important because they tell us something about the thing they are on. For example, imagine a big statue in a park. If there is an inscription on the statue, it might tell us who the statue is meant to represent.
Sometimes monumental inscriptions can also be used to remember someone who has died. If you visit a cemetery, you might see big stones with writing on them. These are called gravestones, and they usually have the name of the person who is buried there, along with important dates like their birth and death.
Overall, monumental inscriptions are a way of telling stories and sharing important information with people who see these big objects or buildings.