This work stretches from deep prehistoric times up to the 12th century AD and beyond. After a short preamble from the Megalithic to the Bronze Age, scanning Tara’s Golden Age, it deals with Celtic Europe’s decline due to Roman and Germanic conquest. It follows Celtic tribes fleeing to Britain and Ireland, where they set up settlements. Ptolemy of Alexandria’s 2nd-century record debunks early Irish pseudo-history and ratifies the archaic Ulidian Tales. This work exposes the monumental hoax projecting Tara of Meath as the capital of Ireland and the seat of the High Kingship. The work draws on a compelling compilation of acclaimed authors and specialist studies that list the aforesaid as a medieval forgery. Prehistoric Tara had a much older status, an archaic Golden Age. This work tracks extensive research and archaeological analysis into British oppida, from which Celtic Belgic tribes migrated and set up similar oppida in Ireland. A concentration on the early history of these neglected areas was at the core of the early Irish historical records.