The Greeks popularized the idea that slaves should be traded from far away, but the Romans took it to another level. Slaves probably made up 30% of the total Roman population, similar to the percentage of slaves in America at slavery's height. The Romans also invented the plantation, using mass numbers of slaves to work the land on giant farms called latifundia, so-called because they were not fun-dia. The Judeo-Christian world contributed as well, and while we are not going to venture into the incredibly complicated role that slavery plays in the Bible, because I vividly remember the comment section from the Christianity episode, the Bible was widely used to justify slavery and in particular the enslavement of Africans, because of the moment in Genesis when Noah curses Ham, saying, Cursed be Canaan, the lowest of slaves shall he be to his brothers. This encapsulates two ideas vital to Atlantic slavery. One, that slavery can be a hereditary status passed down through generations, and two, that slavery is the result of human sin. Both ideas serve as powerful justifications for holding an entire race in bondage.