A legion was a brigade of about 6000 infantry, with 120 horsemen attached to it. It was recruited from any convenient part of the empire, but only from men already enjoying the rights of Roman citizens, or else from those other provincials who were considered sufficiently homogeneous with the Roman civilisation to stand shoulder to shoulder with such citizens. In being permitted to serve on these terms a man regularly becomes _ipso facto_ a citizen. The qualifications required were that you should be free-born--that is to say, neither slave nor ex-slave--your physique must be good, and your height about 5 feet 10 inches: there must be nothing serious against your record or character as viewed from the Roman standpoint; and, if you were not already a citizen, you must belong to one of those organised communes which were the units of administration and of taxation within the empire. You undertake to serve for twenty years, after which time you will receive an honourable discharge and either a sum of money--at this date apparently about £50--or a grant of land. By ability and character you may rise from private soldier to centurion, that is to say, commander of a hundred, but in ordinary circumstances you can climb no further up the military ladder. If at the end of your term you are still robust and are considered useful, you may, if you choose, continue to serve in a special detachment of "veterans," with lighter duties and with exemption from common drill. The Roman legions would thus be made up for the most part of troops from about 18 to 38 years of age, although a considerable number might be somewhat older.