Prehistoric Ireland spans a period between the first known settlement around 8000 BCE until the emergence of "protohistoric" Gaelic Ireland at the time of Christianization in the 5th century; Christianity had subsumed or replaced the earlier polytheism and other forms of Celtic Christianity by the end of the 7th century.The Norman invasion of the late 12th century marked the beginning of more than 700 years of direct English and, later, British involvement in Ireland.