Every medieval society drew a line between the free and the unfree, but each drew it differently. In Latin Europe most unfree people were serfs rather than slaves: they could not be sold apart from the land they worked and could not leave it without permission, yet they kept some property and could sometimes buy their freedom. England's Domesday Book of 1086 recorded roughly 35% villeins and 9% slaves. After the Black Death, serfdom weakened in the West while it hardened in the East, lasting in Russia until 1861, when over 23 million privately held serfs were freed. In the Islamic world the word mamluk simply means “owned.” From the ninth century, rulers bought boys from the steppe and the Caucasus, converted and trained them as cavalry, and then freed them; in 1250 these former slaves seized power in Egypt and Syria, defeated the Mongols at Ain Jalut in 1260, and chose their sultans by merit rather than lineage — while their own sons were excluded from the system. In Goryeo and Joseon Korea, by contrast, the nobi were bound by birth: under the rule that a child of any unfree parent was unfree, the status passed down generations, and at its peak covered more than 30% of the population. King Gwangjong freed the wrongly enslaved in 956, only for the order to be reversed in 987; government nobi were freed in 1801, hereditary status ended in 1886, and the system was abolished in 1894. Land, barracks and birth: three answers to who could be owned — and how, if ever, one could get out.