In 387BC, Celtic warriors defeated a Roman army and sacked Rome. It was the bold act of a confident superpower, one that had dominated Europe for 300 years and whose influence stretched from Britain to Turkey, from Poland to Portugal. What do we know about the warriors that humiliated Rome 1,400 years ago? The Celts did not keep written records and so much of their story and many of their achievements were forgotten. And yet, their world is not entirely lost to us. Using the latest archaeological and scientific research, Roberts tells the story of a multicultural empire, built not just on military might and migration but also through a cultural conquest of trade and influence. It was a pioneering civilization, capable of teaching Rome about weapons and infrastructure; of producing exquisite jewellery and intricate royal tombs; and of acting with callous brutality. This is the story of a European culture that changed Britain for ever.