Thirteen Knights of the Roman Orthodox Church

The Thirteen Knights of the Roman Catholic Church (ローマ正教十三騎士団 Rōma Seikyō Jūsan Kishidan, lit. Roman Orthodox Thirteen Knights Group) is a group of warriors who are one-shot antagonists of the Toaru Majutsu no Index series. It's an organization comprised of thirteen holy knights of the Roman Orthodox Church who work on behalf of the church to exterminate all threats that are posed to the church such as heretics, traitors, and rogue magicians.

Deep Blood Arc
The Thirteen Knights make their debut in the Deep Blood Arc where they have been sent by the Roman Orthodox Church to hunt down and eliminate Aureolus Izzard, an alchemist and the former Cancellarius (secret secretary) of the church, for his defection from the Roman Church and his alignment with the opposing English Puritan Church. The knights are deployed to Misawa Cram High School where he's currently hidding out at. They're allowed into Academy City by Aleister Crowley and kae it to the school. However, their arrival is left unreported to Stiyl Magnus and he and Touma discover the corpse of the Knight Parisfal.

The initial strike did not end well as one of the members was killed and many others went missing. the next night, the remaining seven knights all gather outside the main building and activate the Georgian Chant. The Vatican activates the chant and the remaining knights all aim it at the school where Aurelous is at and launch it while Touma and Stiyl watch. Aureolus however, uses his Ars Magna to deflect the chant and ends up destroying both the attack and presumably the remaining knights. Afterwards, Izzard is defeated and the knights are left dissolved with the Roman Church reporting on it and weakening their power.

Powers & Abilities
According to Stiyl, the knights were originally based off of the Knights of England and act as the Roman Church counter-part to them. Though, they're second-rate by comparison to the English Knights. Despite this however, the knights are still strong and capable warriors.
 * Basic Abilities: The Thirteen Knights have abilities similiar to that of the Knights of England. They use Christian-based Magic and Spells as their main powers and they focus on armor and swordsmanship. The knights are skilled mainly in magic and swordsmanship which they use to track down and kill traitors and heretics.
 * Holy Weapons: The knights have access to the holy weapons of the Roman Church. One of the weapons is the Heavenly Bow though, it's the only weapon they're seen using in the series.
 * Gregorian Chant: The most powerful weapon they have, the Gregorian Chant (グレゴリオの聖歌隊 Guregorio no Seikatai, lit. Gregorian Choir) is a powerful spell that can level entire areas to waste. It takes up to Seven Members to launch the attack and is chanted by 3,333 monks in St. Peter's Basilica.

Notable Members

 * Vittorio Cassera - Head of the Thirteen Knights and is known as Knight Lancelot.
 * Parisfal - Member of the Knights, he's the only one to ahve been killed during their attack against Aureolus Izzard.