The remarkable prowess of the Mamluk sultanate relied on an intricate hierarchical structure of military slaves with the Mamluk sultan at its helm. Mamluks were purchased, received as gifts or taken as prisoners of war. Initially, most were Turks, Kurds or Mongols, joined by Circassians and Georgians from the 8th / 14th century onwards. Every new Mamluk recruit was put through a complete medical examination to ensure his fitness for service. Once accepted, he learned about Islam and was taught basic Arabic; he was expected to have an unquestioning loyalty to his sultan.