In the year 185BC four Celtic mercenary soldiers serving in Egypt visited the temple at Karnak. They caught what they thought was a fox – it was really a jackal, apparently – and scratched the fact, with their names, on the wall. In the same spirit 2000 years on, Scots, Irish and Welsh soldiers in the service of the Raj would wander in the bazaars of Benares or drink in the dives of Singapore.

The Celts have never had an empire, despite the title of this book. Imperialism requires discipline, self-confidence and respect for authority. These are not Celtic characteristics. Before the rise of the Roman Empire, however, Celtic tribes occupied a territory stretching from Ireland across Europe to the Black Sea. The splendidly dotty theory that they crossed the Atlantic in force and established themselves in North America before 500BC has the boot put firmly into it here, but Britain, France, Spain and Portugal, northern Italy and Yugoslavia were all Celtic spheres.

IN 390BC a Celtic army sacked Rome and set siege to the citadel on the Capitoline Hill, which was saved from surprise in a night attack only by the cackling of the sacred geese, which gave the alarm. In commemoration, for centuries geese were gratefully