Thus among the Romans， during the commonwealth， and even under the emperors， no free citizen was allowed， by contract， to become the slave of another.(3*) It was consistent with the refined laws of that people， which rescinded those unequal contracts where one party had gained an undue advantage， or even obtained an unreasonable profit at the expense of the other， to declare that a bargain by which a man surrendered all his rights to a master， and consequently received nothing in return， should have no support or encouragement from the civil magistrate.
As men begin to experience the happy effects of cultivating the arts of peace， and are less frequently employed in acts of hostility， they have less occasion to acquire any number of slaves by captivity.The influence of civilization upon the temper and dispositions of a people has at the same time a tendency to produce a total revolution in the manner of conducting their military operations.That ancient institution， by which every one who is able to bear arms is required to appear in the field at his own charges， becomes too heavy a burden upon those who are enervated with pleasure， or engaged in lucrative professions； and the custom of employing mercenary troops in defence of the country is therefore gradually established.As an army of this kind is maintained by the government； as the soldiers receive constant pay， which is understood to be a full equivalent for their service； they appear to have no title to the extraordinary emoluments arising from the spoil of the enemy； and therefore the captives， though reduced into servitude， are no longer held as belonging to those particular persons by whom they have been subdued， but to the public， at whose expense and hazard the war is supported.(4*)We may take notice of a similar change in the acquisition of slaves by the sentence of a judge.In rude times， the chief aim of punishment was to gratify the resentment of the private party；and if a person accused of a crime had been found guilty， he was， for that reason， frequently delivered up as a slave to the plaintiff.But upon greater improvement of manners， the interpositions of the magistrate came to be influenced more by considerations of general utility； and as the crimes of individuals were principally considered in the light of offences against the society， it was agreeable to this idea that a criminal should become the slave of the public， and should either be employed in public works， or disposed of in the manner most advantageous to the revenue of the community.
The inhabitants of a civilized country， being thus in a great measure deprived of the primitive modes of acquisition， are obliged to acquire the bulk of their slaves， either by a purchase from their poorer and more barbarous neighbours， or by propagating and rearing from the original stock which they possess.In such a situation， therefore， when we compute the expense attending the labour of a slave， not only the charge of his maintenance， but also the money laid out in the first acquisition， together with all the hazard to which his life is exposed， must necessarily be taken into the account.
When these circumstances are duly considered， it will be found that the work of a slave， who receives nothing but a bare subsistence， is really dearer than that of a free man， to whom constant wages are given in proportion to his industry.
Unhappily， men have seldom been in a condition to examine this point with proper attention， and with sufficient impartiality.The practice of slavery being introduced in an early age， is afterwards regarded with that blind prepossession which is commonly acquired in favour of ancient usages： its inconveniences are overlooked， and every innovation， with respect to it， is considered as a dangerous measure.The possession of power is too agreeable to be easily relinquished.Few people will venture upon a new experiment； and， amidst the general prejudices of a country， fewer still are capable of making it with fairness.
We find， accordingly， that this institution， however inconsistent with the rights of humanity， however pernicious and contrary to the true interest of the master， has generally remained in those countries where it was once established， and has been handed down from one generation to another， during all the successive improvements of society， in knowledge， arts， and manufactures.
The advancement of a nation， in these particulars， is even frequently attended with greater severity in the treatment of the slaves.The simplicity of early ages admits of little distinction between the master and his servants， in their employments or manner of living； and though， from the impetuosity and violence of his temper， they may， on some occasions， be subjected to hardships， he enjoys no great superiority over them， in their dress， their lodging， or ordinary entertainment.By the introduction of wealth and luxury， this equality is gradually destroyed.The various refinements which tend to multiply the comforts and conveniencies of life； whatever contributes to ease， to pleasure， to ostentation， or to amusement， is in a great measure appropriated to the rich and the free， while those who remain in a state of servitude are retained in their primitive indigence.The slaves are no longer accustomed to sit at the same table with their master.They must look upon him as a being of superior order， whom they are seldom permitted to approach， and with whom they have hardly any thing in common； who beholds with indifference the toil and drudgery to which they are subjected， and from whom they can with difficulty procure a scanty subsistence.
Ipse dominus dives operis， et laboris expers， Quodcunque homini accidit lib阹e， posse retur：
Aequom esse putat： non reputat laboris quid sit：
