Christianity is a monotheistic religion based on the life and teachings of Jesus of Nazareth. It originated as a sect of Judaism in the Levant, from where it spread to Europe. Though initially persecuted by the Roman Empire, its adoption as the state religion by Constantine I set it on the course of becoming first Europe's most prominent faith and then that of the whole world. Its adherents are commonly known as Christians, and in the 21st century, it remains the world's largest religion with a huge number of denominations.
Unlike Judaism and Islam, however, it also bears the conviction that Jesus of Nazareth was the messiah which humanity had awaited for and that following the teachings of Jesus would result in mankind achieving eternal peace in the Kingdom of Heaven. In Christianity, Jesus himself is God, a doctrine encapsulated in the doctrine of Trinity where though there is one God, God is of three distinct persons: the Father, the Son (Jesus Christ), and the Holy Spirit. 
Eastern Orthodox church
The Eastern Orthodox church was one of the main branches of Christianity and the Byzantine Empire. After the fall of the Byzantine Empire, the church had as Patriarch Pachomius I of Constantinople, who was hated by the Templars, and became the target of the Byzantine Rite. Master Assassin Ezio Auditore da Firenze killed Cyril of Rhodes and prevented the Patriarch's assassination. 
Jesus Christ was a legendary man from Nazareth, near Jerusalem, who was renowned for his divine wisdom and a number of miracles which are believed to have been the work of the Shroud of Eden, which everyday people know as the Shroud of Turin. Deified after his death, his most remarkable feat is said to have been reviving to life three days after his crucifixion by the Roman Empire. His legacy was kept alive by his disciples. By the 5th century, Christianity had become central to Byzantine politics and society; by the 11th century, it pervaded every aspect of European life. Churches, places of worship for this faith, were built in virtually every European city, with the largest cities like Constantinople, Paris, London, and Rome boasting the architectural marvels that are cathedrals. Rome became the capital of Christendom when its bishop was established as the Pope, the supreme authority on Christen doctrine and the community's link with God.
Religious persecutionsReligious zealotry, however, became a prevailing issue throughout Christianity's history. The 11th to 14th centuries were the high point of the Crusades, a series of religious wars waged by European Christian armies against Saracen states in the east, principally to conquer the Holy Land. Among the military orders participating in these Crusades was the Knights Templar, actually a front for the millennia-old, secret organization that thereafter became known as the Templar Order. In the 15th century, persecution of non-Christians escalated with the Spanish Inquisition, where Jews, Muslims, and atheists alike were purged as heretics and burned to death in public. Meanwhile in Florence, the Dominican monk Girolamo Savonarola used an Apple of Eden to seize power and impose his fundamentalist vision by forcing residents to destroy works of art and literature at pain of death.
Corruption under the Borgia
Simultaneously, the Roman Catholic Church became rife with corruption even while it patronized the Renaissance through artistic wonders like Santa Maria del Fiore, the Basilica di San Marco, and the Sistine Chapel. Cardinals and monks like Archbishop Francesco Salviati, Antonio Maffei, and Stefano da Bagnone took part in the Pazzi conspiracy, murdering Giuliano de' Medici in broad daylight, Others like Ristoro regularly molested courtesans at brothels and even murdered fellow monks who questioned his devotion to his vows. Even outside of Spain, it was not unheard of to find Catholic priests who were wiling take bribes to brand random civilians as heretics and have them arrested and executed.
A great deal of these cases, however, were perpetrated by the Templars. Grand Inquisitor Tomás de Torquemada led the Spanish Rite of the Templar Order while Pope Alexander VI was the Grand Master of the Roman Rite who, prior to his tenure, had orchestrated the Pazzi conspiracy. The Pope presided over an unprecedented level of corruption in the Church, using his Borgia family's influence to extort and shutdown businesses for its own benefit and engage in wanton killings of anyone who offended the Borgia or their patrons, among them scientists, Christian reformers, and women they had violated. Notwithstanding this, he had only become Pope for the purpose of overthrowing God and stealing his power, believing that the being lay dormant in the Vault beneath the Vatican and could be slain by the Pieces of Eden.
The Borgia reign over the Papacy collapsed in 1503 under an active campaign by the Templars' sworn enemies, the Assassin Brotherhood, to liberate Rome. Tensions between the Catholic Church and common Christians did not end there however. Pope Julius II, earning the epithet "the Warrior Pope", actively engaged the Papal States in wars of domination over Italy that were not unlike the conquests of Cesare Borgia,  who he had a hand in arresting. His successor, Leo X, was an ally of the Assassins but was also notorious for the commercialization of indulgences, selling absolution from sins.
Church practices such as these alienated Christian scholars who agitated for reforms. Among the most notable were Desiderius Erasmus, a prior target of the Borgia, and Martin Luther, an archenemy of Leo X.  The two were at odds; Erasmus had become an Assassin of the North European Brotherhood and had written a letter in 1512 warning Mentor Ezio Auditore da Firenze of Luther's radicalism. In 1517, Luther nailed his famous Ninety-five Theses denouncing Catholic Church onto the door of a church at the University of Wittenberg, kick-starting the Protestant Reformation. 
The movement triggered more than a century of religious warfare in Europe as governments and families alike increasingly found themselves divided between Catholicism and Protestantism. The schism played a prominent role in the English Civil War of the mid-17th century, with Catholics largely siding with the monarchy and Protestants siding with the Parliamentarians. 
By way of the European colonial empires, particularly the Spanish and the British Empires, Christianity spread to the Americas and grew in prominence in Africa and Asia.  The thirteen British American colonies which seceded as the United States of America in the late 18th century was already heavily Protestant at the time of its revolution as a result of its cultural and political history. At the same time, the faith faced new challenges in Europe owing to the rise of Enlightenment ideas; a significant segment of Parisian society professed to atheism during the French Revolution, rebelling against the church. Nonetheless, Christianity remains the largest religion on Earth in the 21st century. 
Its troubled history likely weighed on the mind of the Assassin Desmond Miles when, on 21 December 2012, he was presented with the choice of either sacrificing his life to save humanity from a coronal mass ejection or surviving to become a leader to the few populations of survivors. In the vision he was shown by Minerva and Juno, he witnessed his future in the latter course, where he would become an exalted hero whose teachings of love and peace would inspire the hearts of many and lead to a rebirth of civilization, but in death, that love would become zealotry and dogma. Eventually, he would become deified by later generations, and the very memory of him as a saviour would be twisted into an icon to justify persecution, violence, and oppression. The vision echoed Jesus's legacy, and Juno even drove home the point that for Desmond to choose that route would mean renewing the cycle. With his mind set, Desmond touched the Eye that would activate the planetary shield at the cost of his life, thereby saving the world.
- Assassin's Creed
- Assassin's Creed II
- Assassin's Creed: Project Legacy
- Assassin's Creed: Brotherhood
- Assassin's Creed: Revelations
- Assassin's Creed III
- Assassin's Creed: Rogue
- Assassin's Creed: Unity
- Assassin's Creed: Syndicate
- ↑ 1.0 1.1 Assassin's Creed II – In Bocca al Lupo
- ↑ Assassin's Creed: Revelations
- ↑ 3.0 3.1 3.2 Assassin's Creed II
- ↑ 4.0 4.1 4.2 4.3 Assassin's Creed: Brotherhood
- ↑ 5.0 5.1 Assassin's Creed: Unity
- ↑ Assassin's Creed: Syndicate
- ↑ Assassin's Creed
- ↑ Assassin's Creed II: Discovery
- ↑ Assassin's Creed: Rebellion
- ↑ Assassin's Creed II – Bonfire of the Vanities
- ↑ Assassin's Creed II – Wolves in Sheep's Clothing
- ↑ Assassin's Creed: Project Legacy – Rome: Chapter 1 – Fiora Cavazza
- ↑ Assassin's Creed: Brotherhood – Excommunication
- ↑ Assassin's Creed: Project Legacy – Italian Wars: Chapter 2 – Francesco Vecellio
- ↑ Assassin's Creed: Project Legacy – Rome: Chapter 3 – Francesco Vecellio
- ↑ Assassin's Creed: Brotherhood] – Copernicus Conspiracy
- ↑ 17.0 17.1 Assassin's Creed: Project Legacy – Contracts
- ↑ Assassin's Creed: Brotherhood – Well Executed
- ↑ Assassin's Creed: Brotherhood – All Roads Lead To...
- ↑ 20.0 20.1 Assassin's Creed: Revelations novel
- ↑ 21.0 21.1 Assassin's Creed III