Who exactly were the Celts? That’s the question at the jewel-encrusted heart of the British Museum’s new blockbuster. The short answer is that they were, initially, a disparate lot, hailing from central Europe and setting up shop – or more likely, from the look of the exhibition, setting up workshops – in other parts of Europe including Wales, Scotland, Cornwall and the Isle of Man.By the eighth century the Northumbrian monk St Bede was describing them as four peoples and four languages, and noting that there was now a fifth language, Latin, which united them all in the new-found Christian faith. These two factors – Latin and Christianity – linked the scattered Celtic communities, and nowhere was this linkage more evident than in their art. This, it tra