Slaves | Wealth and resources were divided unequally during the empire, with relatively little social mobility. The large labor force consisted of slaves and poorly paid freedmen nearly indistinguishable from slaves. Debt landsmen and peasants tied down to the land were also not technically considered slaves. In the Roman world, slaves and their children were the property of the owner, sold and rented out by dealers and exchanged between individuals. Slaves had always been used in Rome, but there was a sharp increase in their numbers after the 2nd century BC. Slaves could be obtained as prisoners of war or through trade outside of Roman territory. Parents also had the right to sell their children as slaves to pay off debts. Homebred slaves eventually outnumbered those who had been free before and were enslaved. Therefore, slaves became expensive and unprofitable to use in unskilled labor, and he was eventually replaced by free labor in mines and other industry. Indeed, slaves were employed in almost every form of skilled and unskilled labor, and performed the "overwhelming" amount of work on mining, manufacture, and private labor. The state owned slaves too, for the purpose of maintaining public works such as roads and aqueducts, but was limited by the practice of contracting out public enterprises. The agricultural labor force was far more complex, with farming estates worked wholly by slaves as well as those owned by peasants or leased out to tenants. Treatment of slaves greatly varied. Harsh treatment was usually restrained, as he doing the punishing had to keep in mind he was damaging his own "investment." Treatment was typically more brutal in agriculture, mining, and factories, where slaves might work seven days weekly without holiday. Evidence exists to indicate that slaves were worked in chain gangs and locked away at night,