When different groups of people lived in what is now Italy a long time ago, they had their own leaders and rules. But eventually, a group of people called the Romans took over most of the area and started their own way of governing.
Instead of having just one leader, like a king, the Romans decided to have a group of leaders called senators. These senators were chosen by the people and were in charge of making decisions for the whole group.
The Romans also had a system where every citizen (a person who belonged to the group) could vote on certain things, like who should be a senator or what laws should be made. This way, everyone had a say in what was happening.
The Roman Republic lasted for around 500 years, but eventually they started having some problems. The leaders (senators) became corrupt and only cared about their own power instead of making decisions for the good of the people. Also, not everyone in the group was treated equally - some people were slaves and had no say in what happened.
Despite these problems, the Roman Republic was an important step in the development of democracy (a way of governing where everyone has a say). Many of the ideas they came up with were later used in other countries around the world.