Edward Gibbon, The Decline and Fall of the Roman Empire

In the purer ages of the commonwealth, the use of arms was reserved for those ranks of citizens who had a country to love, a property to defend, and some share in enacting those laws, which it was their interest, as well as duty, to maintain. But in proportion as the public freedom was lost in extent of conquest, war was gradually improved into an art, and degraded into a trade. The legions themselves, even at distant provinces, were supposed to consist of Roman citizens. That distinction was generally considered either as a legal qualification or as a proper recompense for the soldier; but a more serious regard was paid to the essential merit of age, strength, and military stature. In all levies, a just preference was given to the climates of the North over those of the South: the race of men born to the exercise of arms was sought for in the country rather than in cities; and it was very reasonably presumed, that the hardy occupations of smiths, carpenters, and huntsmen , would supply more vigour and resolution than the sedentary trades which are employed in the service of luxury. After every qualification of property had been laid aside, the armies of the Roman emperors were still commanded, for the most part, by officers of a liberal birth and education; but the common soldiers, like the mercenary troops of modern Europe, were drawn from the meanest, and very frequently from the most profligate, of mankind.

That public virtue which among the ancients was denominated patriotism, is derived from a strong sense of our own interest in the preservation and prosperity of the free government of which we are members. Such a sentiment, which had rendered the legions of the republic almost invincible, could make but a very feeble impression on the mercenary servants of a despotic prince; and it beame necessary to supply that defect by other motives, of a different, but not less forcible nature; honour and religion. The peasant, or mechanic, imbibed the useful prejudice that he was advanced to the more dignified prfession of arms, in which his rank and reputation would depned on his own valour; and that, although the prowess of a private soldier must often escape the notice of fame, his own behaviour might sometimes confer glory or disgrace on the company, the legion, or even the army, to whose honours he was associated. On his first entrance into the service, an oath was administered to him, with every circumstance of solemnity. He promised never to desert his standard, to submit his own will to the commands of his leader, and to sacrifice his life for the safety of the emperor and the empire. The attachment of the Roman troops to their standards was inspired by the united influence of religion and of honour. The golden eagle, wihch glittered in the front of the legion, was the object of their fondest devotion; nor was it esteemed less impious than it was ignominious, to abandon that sacred ensign in the hour of danger. These motives, which derived their strength from the imatgination, were enforced by fears and hopes of a more substanial kind. Regular pay, occasional donatives, and a stated recompense, after the appointed time of service, alleviated the hardships of the military life, whilst, on the other hand, it was impossible for cowardice or disobedience to excape the severest punishment. The centurions were authorized to chastise with blows, the generals had a right to punish with death; and it was an inflexible maxim of Roman discipline, that a good soldier should dread his officers far more than the enemy. From such laudable arts did the valour of the Imperial troops receive a degree of firmness and docility, unattainable by the impetuous and irregular passions of barbarians.

[Chapter 1, "The Extent and Military Force fo teh Empire in the Age of the Antonines"]