Aztec Slave Market-The Aztecs additionally had landless serfs and slaves. Serfs worked land that was owned by nobles and did not live in the calpulli. Individuals became slaves (tlacotin) as a form of punishment for certain crimes or for failure to pay tribute. Prisoners of war who were not used as human sacrifices became slaves. An individual could voluntarily sell himself or his children into slavery to pay back a debt (the latter required permission of the court).