Nobody knows exactly when the first people came to Ireland. Using radiometric dating, scientists found that a bear bone with knife marks was 12,500 years old. It is likely that people lived in Ireland then. By 7900 BCE, hunter-gatherers (people who ate wild plants and animals) lived in Ireland. This time was called the Stone Age. Around 4000 BCE, they started making farms with animals and plants. They made pottery, stone tools, wood houses, and large tombs. The Bronze Age started around 2500 BCE. People learned to make things out of metals like bronze, gold, and copper, but it was mostly only rich people who had them. People also started weaving and working with leather. Large rooms were built to store metal weapons. The Iron Age started around 600 BCE or earlier, when people started making iron tools. During the Iron Age, Celts came to Ireland, so they started speaking Celtic languages. The Celts brought their style of art with them. Between 1 and 400 CE, Roman soldiers may have invaded Ireland, but Ireland did not join the Roman Empire. About five kings each ruled a large part of Ireland.