Roman Catholic Church

The Roman Catholic Church (ローマ正教) is the world's largest Christian organization, boasting a number of 2 billion worshippers, spanning across 113 countries. It is one of the three major Christian denominations, alongside the Anglican Purist Church and the Russian Orthodox Church.

Their central base is the Vatican City State, protected by a barrier that incorporates a magical formation that involves 90% of the buildings in Rome, and a 'lock' that changes every hour, a security which supposedly not even Index Librorum Prohibitorum can break through.

Etymology
The word catholic is derived from the Greek word καθολικός (katholikos), which means "universal".

However, the author uses a naming convention of having the Churches named after a place and adding its quality, in this case, the proper name of the Roman Catholic Church is Roman Orthodox Church in the Toaru Majutsu no Index setting.

Principles
Accoding to Index, the Roman Catholic Church's role in the magic side is to "manage and control the world". It is one of the oldest types of Christianity, having coalesced in the 4th Century AD after the Roman government began allowing Christians to practice openly. The leader of the Catholic Church, the Pope, is the Bishop of Rome just as St. Peter was.

The Ten Holy Spirit Spells
The Ten Holy Spirit Spells (聖霊十式) are some of the most powerful spells that the Roman Catholic Church has in their possession, though not all ten are shown yet in the novels.

Croce di Pietro
"Croce di Pietro" (使徒十字 (クローチェディピエトロ)), mistaken for the "Stab Sword" (刺突杭剣 (スタブソード)) in Volume 9, an artifact used 'to pierce the dragon and pin it down on the Earth'. It was revealed to what it really is in Volume 10, it's a artifact that 'changes both the spiritual and physical aspects of the land it was raised to be beneficial to the Roman Catholic Church in every way'. The 'Stab Sword' that it was mistaken for never existed, just a propaganda made by the RCC as another layer of defence to protect this artifact. The reasoning behind this is a dragon is a powerful winged being that guards treasures that's slumbering away from the world and kills indiscrimately, symbolising the 'Angels' and the fallen ones, the 'Demons'. 'Pinning the dragon down on the Earth' also means 'to have the Angels guard this land to make it a Holy place'.

Named after one of the 12 Apostles, and the artifact that created the Vatican to what it is now when it was raised after Saint Peter's Death. Supposedly shattered when it fell out of a plane and into the sea at the end of volume 10. Also called as "The Cross of St. Peter".

In Real Life, the Cross is also known as the Petrine Cross, is an inverted Latin cross traditionally used as a Christian symbol, but in recent times also used widely and incorrectly as an anti-Christ symbol, a common misconception. This might not be the case in Index canon.

La Regina del Mare Adriatico
In english, "The Queen of the Adriatic Sea" was made during the period where Rome and Venice were separate states and are hostile towards each other. This is a large area spell that the Roman Catholics created back when they weren't getting along well with Venice. Afraid of the Venetian Navy, the Roman Catholics came up with a counter measure should Venice ever attack - La Regina del Mar Adriatico - A weapon that could destroy Venice in an instant. In order to prevent their own weapon from being used against them, the Roman Catholics set a restriction within the spell, allowing it only to be used on Venice and nowhere else. The first phase of the attack is to bombard the major centers of the city. The second phase is the utter destruction of the knowledge, technology, historical artifacts of Venice, essentially wiping out their culture from the face of the Earth. It has a limited range of 10 miles. In order to protect themselves from possible attackers while casting the spell, the Roman Catholics also created a fleet of ships made out of ice form from the surrounding sea water. The fleet has a maximum cannon range of 5 km, but more importanly, if any of the ships are damaged or destroyed, they can simply regenerate using the water. The real form is a magical attack that's similar to the judgment of 'Power of God' (Gabriel) that destroyed Sodom and Gomorrah, that if used would completely destroy Venice and all it's traces from history, including it's art and people.

In Volume 11 the Roman Catholic Church attempted to remodel this artifact so that it can target something apart from Venice, namely Academy City, but were stopped by a group consisting of Kamijou Touma, Index, Orsola Aquinas and the Amakusa Church. Destroyed by Kamijou Touma in Volume 11, when he destroyed the core cross in his fight with the main antagonist of that volume, Bishop Biagio Busoni.

In Volume 20, Vento of the Front reconstructed the core and holds partial control over the Queen of Adriatic through a new cross on her tongue made of ice and shaped like a anchor. In her words this is possible as Wind, her element, is a crucial part of sailing so she can have control over water-based spells. However after using the cannons to attack Fiamma she had the ice cross ripped out of her tongue by Fiamma and she no longer have this ability.

Ironically, the term "Queen of the Adriatic (Sea)" is sometimes used to refer to the Italian city Venice. This is intentional, as the Roman Catholic Church specifically designed this spell to wipe out Venice and this is a statement that 'Venice is not more powerful than Rome'.

Gregorian Chant
A weapon similar to orbital bombardment, where 3,333 monks chant from holy scriptures inside the Vatican and focus the energy into a beam that can strike almost anywhere on Earth. Said to be the Roman Catholic Church's ultimate weapon, until one of its strikes got reflected back by Auroleus Izzard's Ars Magna in volume 2 of the novels.

Also referred to as "Gregorio's Chant", using the Italian translation for Gregory, "Gregorio". The term is originally used for a form of liturgical music in Western Christianity Masses and rituals as primary accompaniment.

Document of Constantine
Also known as the C-Document, it's power is "to make whatever the Pope says seem to be the absolute truth", and the cause of general unrest around the world in volume 14. Destroyed by Kamijou Touma in Volume 14.

A similar piece of documents relating to the Holy Roman Emperor Constantine I, the "Donation of Constantine", supposedly transferred authority over Rome and the western part of the Roman Empire to the pope. This, however, is a forgery dating between the 8th and 9th Centuries CE.

God's Right Seat
God's Right Seat is a organisation within the Roman Catholic Church originally supposed to guide the Pope on matters beyond human knowledge when first created, though now it has changed to being a organisation whose members wields more power than the Pope. In later novels this organisation is the main antagonist in the conflict between the Magic side and Science side.

Other Notable Aspects

 * The Roman Catholic Church also possesses the Book of the Law, a grimoire written by the most renowned magician in his time, Aleister Crowley.
 * The Roman Catholic Church also have magical Knights, an idea borrowed from the Knights of England. Necessarius member Stiyl Magnus remarked they are second-rate amateurs compared to the originals.