Thirteen Knights of the Roman Catholic Church

The Thirteen Knights of the Roman Catholic Church (ローマ正教十三騎士団) is a group of warriors created by and serve under the Roman Catholic Church. According to Stiyl Magnus, the Thirteen Knights are simply a poor imitation of the Knights of England.

Their primary purpose appears to be hunting down and eliminating threats and rogue magicians, like Aureolus Izzard.

Deep Blood Arc
The knights were sent to take care of Aureolus after he was discovered to have taken over Misawa Cram School. They were allowed to enter Academy City by General Superintendant Aleister, though their entrance wasn't told to Stiyl Magnus and he found out when he saw a knight's corpse.

The initial strike did not go well, as one member was killed, as his corpse was found by Touma and Stiyl. The next night, the remaining members tried to destroy the building Izzard was by marking the Misawa Cram School so the Gregorian Chant launched by the Vatican can strike at Aureolus Izzard from afar. However, the spell was bounced back by Aureolus using his Ars Magna, destroying the Gregorian Chant.

Abilities
According to Stiyl, while the Thirteen knights were based off of the Knights of England, compared to their English counterparts the Roman knights were second-rate amateurs. These knights seem to have the same kind of skills as the Knights of England, focusing on heavy armor while attempting to be skilled in both magic and swordsmanship.

They also possess duplicates of holy weapons, such as a Heavenly Bow.

Their most notable ability is to use the Gregorian Chant, a powerful long range bombardment spell that is chanted by the 3,333 monks in St. Peter's Basilica. It is capable of destroying an entire building in one blow. It is shown that at least 7 knights are needed to cast the spell.

Known members
Since their introduction, there is currently only one named member of the knights. It is also apparent that knights are named after the of.
 * Knight Parsifal (real name unknown) - The knight that Touma and Stiyl found dead when they entered Misawa Cram School.
 * Knight Lancelot (Vittorio Cassera)

Trivia

 * It's unknown if the knights had the same duties as the Agnese Forces, though it seems likely.