To be fair, the Templars were different from the other major international military orders. Uniquely, from the beginning they were knights who took up a religious calling, rather than servants of a hospital that added a paramilitary wing. This gave them a certain quality that was useful for medieval romance: they corresponded exactly to the archetype of the truly chivalrous knight: violent but chaste, tough but pure of heart, merciless but godly. They were the ideal that all knights in Arthurian legend strove towards.
