The Mauryan army of India would have been a heart-stopping sight for enemies as it numbered more than 600,000 men, 30,000 cavalry and 9000 elephants.

The ancient Irish were part of a highly sophisticated society that bred musicians, farmers, druids and brave warriors.

The clans of the Scottish highlands were hardy people and the men fought hard to maintain their independence from all comers.

Just the name was enough to strike fear into the hearts of Europeans and the wide-ranging trail of these fierce pagan raiders was littered with cruel violence.

These Christian warrior-monks were sworn to a life of poverty and chastity - as well as one of ridding the Holy Land of all Muslims.

The hordes that swept across Europe were more than just wild tribesmen - they were a highly trained and disciplined army of conquerors.

Originally captured Christian slaves, the Janissaries became some of the most feared troops of the Muslim world.