Overall, the Celtic term applies to people who lived in Britain and Western Europe between 2000 BC and 400 AD. They were civilizations from the Iron Age, especially residents of small villages led by warlords. The Celts of continental Europe left no written record, but we know their gods through the Roman conquerors, who established links between many of these deities and their own gods. For example, the thunder god Taranis was the equivalent of the Roman Jupiter, and several other local deities were treated as Mars, Mercury and Apollo. The country’s people of Wales and Ireland have also left a rich mythology and many of his tales were written during the Middle Ages.