The Knights of St. John (AKA the Knights Hospitalier, or the Knights of Malta ) were one of the special religious orders formed in reaction to the Muslim invasions, and prominent in the Crusades (with the Templars and Teutonic Knights).
As a religious order, one of their commitments was a substantial daily recitation of prayers. Since the siege of Malta was long and they had little time to themselves, they were reported to have sung out their prayers together for hours on end, even while engaged in heavy combat.
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