 Troops in all of these classes would fight together on the battlefield, with the exception of the most senior troops, who were expected to guard the city.The army is said to have increased from 3,000 to 4,000 men in the 5th century BC, and then again from 4,000 to 6,000 men sometime before 400 BC.This later army of 6,000 men were then divided into 60 "centuries" of 100 men each.