One Roman legion founded by Augustus was still serving in Egypt six centuries later
Legio V Macedonica, raised by Augustus in 43 BC, was still on duty in Egypt during the Islamic conquest of the seventh century. Three of his other legions had the opposite fate: wiped out by Arminius in AD 9, their numbers were never used again. The legion was an institution that could outlive dynasties.
What a legion was changed enormously. In the early kingdom the word may simply have meant the whole Roman army, and legend credits King Servius Tullius with a census sorting property-owning men into five wealth classes for service. Under the Republic, legions were raised only when war threatened, normally four at a time, two per consul. Soldiers had no career path and little pay, relying on plunder, and went home when the campaign ended.
Tactics were rebuilt after a crushing defeat at the Allia in 387 BC. At first the lines were ordered by wealth, with the poorest in front carrying spears and big rectangular shields, and the richest at the back fighting like Greek hoplites. By the 3rd century BC that seemed inefficient, so ranks were rearranged by age and experience, every man got a short sword and two throwing javelins, and poorly equipped skirmishers called velites screened the heavy infantry. The historian Polybius, writing about 150 BC, gives the earliest detailed description.
From roughly 100 BC the legion was reorganised into ten cohorts made up of centuries of 80 men. By imperial times a field strength of around 5,280 was typical, with the first cohort almost double the size of the rest. Legionaries were the elite heavy infantry and had to be citizens; most of the army, including nearly all the cavalry, was actually made up of auxiliaries, provincials who earned citizenship on honourable discharge.
The Varian Disaster of September AD 9 destroyed the Seventeenth, Eighteenth and Nineteenth Legions in Germany, and a famous line has Augustus crying out for Varus to return them. Later the big formations were broken into smaller detachments to cover more ground, and by the fourth century a legion numbered perhaps 1,000 to 1,500 men, with eastern border garrisons possibly smaller still.
Source: Roman legion
