Decemviri were a group of ten very important people who lived a very long time ago in ancient Rome. They were chosen to make laws that all the people in Rome had to follow.
Think of decemviri like a group of ten people who are chosen to play a game of make-believe. They all agree on the rules of the game and make sure that everyone plays by these rules.
However, if any of the people in Rome broke the laws that the decemviri made, they would be punished. This punishment could be really harsh, like getting thrown in jail or losing their property.
So, decemviri were like super important people who helped keep everything in order and made sure everyone followed the rules. They were kind of like bosses of ancient Rome!