How far back has slavery existed?

Since the dawn of time there has been slavery. One of the most ancient practice was to take slaves as part of war. The winners took women and children as slaves and the men who surived the war were taken as slaves. The Romans made the POW's the gladiators for the arena. They didn't fight because they were paid for it. They were slaves. Throughout the ancient world slaves were bought and sold in markets in the cities of the ancient world. Slavery still exists today with women and children sold as sex slaves throughout the world.