This is a great question. During the Roman Republic there were a number of ways in which slaves were acquired. In fact, Rome was one of the great slave societies in the history of the world. In light of this, here are the major ways in which slaves were gotten:
- Prisoners of war were the most common way in which to acquire slaves. Even the Latin word, "servus," which means spared one, suggests this. A general spared a life and now this life was owned. Each battle can create many slaves. For example, in the fall of Veii early 4th century, there were 5000 slaves; And in 168 BC the Romans got 150,000 slaves from the battle with Epirus in one day.
- Children born to slaves were also considered slaves of the master.
- During the early Republic, people could be sold into slavery on account of debt.
- Exposured children could also be sold into slavery.
- Finally, there were many brigands and pirate who actually sought slaves to make a profit.