The Behistun Inscription is a really old writing that tells a big story about a king named Darius and how he defeated some other guys who were trying to take over his kingdom a long, long time ago.
The story was written on a really big and tall rock wall that is still there in Iran today. It's like a giant history book carved into the side of a mountain!
The writing is in a special language that was used a long time ago, and it tells people about important things that happened in the past. The people who wrote it wanted to make sure everyone knew the story, so they put pictures and words all over the wall.
Some very smart people studied this writing and figured out what it said, which helped us understand more about how people lived a really long time ago. It's kind of like a puzzle that they had to solve in order to understand the story.
So, the Behistun Inscription is like a really old "history book" that teaches us about things that happened a long time ago, and how people recorded important stories in the past.