The historical phenomenon of Christianization, (or Christianisation - see spelling differences) the conversion of individuals to Christianity or the conversion of entire peoples at once, also includes the practice of converting native pagan practices and culture, pagan religious imagery, pagan sites and the pagan calendar to Christian uses, due to the Christian efforts at proselytism (evangelism) based on the tradition of the "Great Commission".
The process of Christianization has at times been relatively peaceful and at times has been a very violent process, ranging from political conversions to adopt Christianity to military campaigns to force conversion onto native populaces.
In Antiquity, Christianization was effected only partly through laws against indigenous religious practices, official conversions of temples to Christian churches and the placement of Christian churches over ancient religious sites. It was effected also by the demonization of indigenous pagan gods, traditional practices into witchcraft and the partial Christianization to outright banning of existing rites under threat of torture and death.
Reformatting native religious and cultural activities and beliefs into a Christianized form was officially sanctioned; preserved in the Venerable Bede's Historia ecclesiastica gentis Anglorum is a letter from Pope Gregory I to Mellitus, arguing that conversions were easier if people were allowed to retain the outward forms of their traditions, while claiming that the traditions were in honour of the Christian God, "to the end that, whilst some gratifications are outwardly permitted them, they may the more easily consent to the inward consolations of the grace of God". In essence, it was intended that the traditions and practices still existed, but that the reasoning behind them was forgotten. The existence of syncretism in Christian tradition has long been recognized by scholars, and in recent times many of the instances of syncretism have also been acknowledged by the Roman Catholic church.
Humanistic studies of Antiquity and the Reformation combined in the sixteenth century to produce works of scholarship marked by an agenda that was occupied with identifying Roman Catholic practices with paganism, and identifying the emerging Protestant churches with a purgative "re-Christianization" of society. The Lutheran scholar Philip Melanchthon produced his Apologia Confessionis Augustanae (1530) detailing the rites derived from pagan practices. Heinrich Bullinger, De origine erroris libris duo (1539) detailed the pagan "origins of (Catholic) errors".
Isaac Casaubon, De rebus sacris et ecclesiasticus exercitationes (1614) makes a third familiar example, where sound scholarship was somewhat compromised by sectarian pleading. Thus such pagan precedents for Christian practice have tended to be downplayed or even sometimes dismissed by Christian apologists as a form of Protestant Apologetics.
The 20th century saw more purely historical inquiries, free of sectarian bias; an early historicist classic in this field of study was Jean Seznec's The Survival of the Pagan Gods: the mythological tradition and its place in Renaissance humanism and the arts. (1972).
Although the cross is currently the most common symbol of Christianity, and has been for many centuries, it only came to prominence during the fourth century, and was not particularly associated with Christianity before that time. According to Christian tradition, the cross is a reference to the crucifixion of Jesus, and the crucifix is a more obvious, and some would say gruesome, version of such a reference. However, due to the highly ambiguous nature of the Greek terms used in the bible for his crucifixion, it may be the case that the correct translation actually points to Jesus having just been tied to a single stake of wood, rather than the cross shaped device in traditional depictions; though Christian translations into English often render these terms as nailed to a cross, they could equally mean nailed to a tree and nailed to a wooden pole, which was another common method of crucifixion in the Roman empire - the hands being tied above the head.
Crosses, however, were important symbols of several pre-Christian religions, including Hinduism where the Swastika was originally a prominent holy symbol and the religion of Ancient Egypt where the increasingly cross-shaped Ankh was regarded as a symbol of life itself. The main early Christianity communities centred on Alexandria and Rome, and it is thought likely that the Alexandrian Christians adopted the Ankh, while the Rome-based Christians adopted the cross from influences such as depictions of Bacchus with his head covered by cross symbols. Those who see Jesus as simply a Jewish form of the Osiris-Dionysus mythology consider the use of the Ankh symbol as an obvious continuation, while other scholars consider that it was adopted due to Christianity valuing its metaphysical connotations.
The predecessor of the cross as the main Christian symbol was the labarum, a symbol formed by overlaying the first two letters of the Greek word for christ in the Greek alphabet. Constantine I is widely considered to have introduced the symbol into Christianity, but the symbol itself predates this, and was also used by the major religion of Sol Invictus, due to its prior use as a major symbol representing good fortune. Prior to Christianity, the symbol had become considered to represent auspiciousness since it was earlier the symbol of Chronos, the Greek deity of time itself, whose name it forms the monogram of, in much the same way as it monograms an epithet given by Christians to Jesus.
Although Christian tradition argues that Constantine chose the labarum because he had a vision that lead him to convert to Christianity, Constantine's conversion is disputed by many historians since he continued using clearly Sol Invictus related symbolism and wording on his currency for much of the remaineder of his life, remained the Pontifex Maximus of Mithraism/Ancient Roman religion for his entire life, and was only baptised on his deathbed (although this was common at the time; many Christians believed that if one sinned after baptism one's salvation was lost), and even that is disputed since the only witnesses were the same people that claimed that Constantine had been Christian for much longer. Most secular historians see Constantine's motive for choosing the labarum as political rather than supernatural or religious, with him deliberately making his banner one which could be interpreted as supporting either of the two major religions of the Roman Empire at the time; Constantine saw unity and conformity as the way to achieve political stability, and spent a great deal of time attempting to reduce division (for example by holding the First Council of Nicaea to settle the question of Arianism). Although many Christian groups treat the symbol as having always been exclusively Christian, certain Protestant groups, particularly Restorationists support the conclusions of secular scholars, and consequently regard the symbol as non-Christian, disowning it.
Prior to the labarum, the main Christian symbol, and the earliest, was a fish-like symbol now known as Ichthys (the Greek word for fish); the Greek word ιχθυς is an acronym for the phrase transliterated as " Iesou Christos Theou Yios Sotiras," that is, "Jesus Christ, God's Son, the Savior." There are several other connections with Christian tradition relating to this choice of symbol: that it was a reference to the feeding of the multitude; that it referred to some of the apostles having previously been fishermen; or that the word Christ was pronounced by Jews in a similar way to the Hebrew word for fish (though Nuna is the normal Aramaic word for fish, making this seem unlikely).
See main article: Christianised sites. Few Christian churches built in the first half millennium of the established Christian Church were not built upon sites already consecrated as pagan temples or mithraea, the church of Santa Maria sopra Minerva (literally Saint Mary above Minerva) in Rome being simply the most obvious example. Sulpicius Severus, in his Vita of Martin of Tours, a dedicated destroyer of temples and sacred trees, remarks "wherever he destroyed heathen temples, there he used immediately to build either churches or monasteries" , and when Benedict took possession of the site at Monte Cassino, he began by smashing the sculpture of Apollo and the altar that crowned the height.
The British Isles and other areas of northern Europe that were formerly druidic are still densely punctuated by holy wells and holy springs that are now attributed to some saint, often a highly local saint unknown elsewhere; in earlier times many of these were seen as guarded by supernatural forces such as the melusina, and many such pre-Christian holy wells appear to survive as baptistries. Not all pre-Christian holy places were respected enough for them to survive, however, as most ancient European sacred groves, such as the great Irminsul (whose location is now lost, but was possibly located at Externsteine), were destroyed by Christianizing forces.
During the Reconquista and the Crusades, the cross served the symbolic function of possession that a flag would occupy today. At the siege of Lisbon in 1147, when a mixed group of Christians took the city, "What great joy and what a great abundance there was of pious tears when, to the praise and honor of God and of the most Holy Virgin Mary the saving cross was placed atop the highest tower to be seen by all as a symbol of the city's subjection."
See main article: Christianised Myths and Imagery. The historicity of several saints has often been treated sceptically by most academics, either because there is a paucity of historical evidence for them, or due to striking resemblances that they have to pre-Christian deities. In 1969 the Roman Catholic church officially decanonised some Christian Saints, demoted others, and pronounced the historicity of others to be dubious. Though highly popular in the Middle Ages, many of these such saints have since been largely forgotten since, and their names may now seem quite unfamiliar. The most prominent amongst these is Saint Eustace, who was extremely popular in earlier times, but scholars now see as a chimera composed from details of several other Saints. Many of these figures of dubious historicity appear to be based on figures from pre-Christian myth and legend, Saint Sarah, for example, also known as Sarah-la-Kali, is thought by scholars to be a Christianization of Kali, a Hindu deity.
Other more obviously Christian figures, such as certain bishops whose existence are widely attested in historic literature, and central figures such as Mary, the mother of Jesus, Michael, the archangel, and Satan, are not however, without later legendary additions to their more historic narratives. Not only are there apocryphal writings such as the Home-going of the holy Mary (about her death), but much iconography associated with certain figures, such as with Michael and with Mary, is suspected by several historians to be Christianization of earlier iconography that originally concerned other, non-Christian, figures. The similarity of Christian depictions of demons to several pre-Christian deities, and deity-related figures such as Satyrs, has led several scholars to argue that the stereotypical Christian depiction of Satan, and of demons in general, was deliberate demonisation of benign figures from rival religions.
See main article: The Christianised calendar. Several Christian feasts occupy moments in the year that were formerly devoted to pagan celebrations. Familiar examples are the Roman Saturnalia, converted to Christmas, the festivities of Yule in northern Europe, the name of Eostre converted to English "Easter" to identify the Paschal festival, the celebration of Midsummer Day as the birthday feast of John the Baptist, and the celebrations of the Feast of the Lemures and of Celtic Samhain combined and transferred to the eve of All Saints' Day a.k.a. Halloween.
Christians in authority frowned upon the riot and disorder of the pre-Christian festivals; in regard to Yule, the friend and biographer of Saint Eligius recorded that the bishop called the "Apostle to the Frisians" would caution his flock [Do not] make vetulas, (little figures of the Old Woman), little deer or iotticos or set tables at night (for the house-elf, compare Puck) or exchange New Year gifts or supply superfluous drinks. However, such pre-Christian activities proved hard to suppress, and several edicts were given that instruct missionaries to attempt to absorb earlier traditions into Christianity so as to distract people from their pre-Christian gods; All Souls' Day was for example accepted by Odilo (died 1048) in the Cluniac monasteries, and its observance spread through the Celtic north before it was introduced into Italy.
See main article: Christianised rituals. The obvious connection to Jewish rituals of Christian practices such as the Eucharist and Baptism, is often argued to be by design. Christian tradition places these Christian use of these activities as having originated in the life of Jesus, as attested by the Biblical narratives (e.g. the Baptism of Jesus for Baptism, and Last Supper for the Eucharist), and the Biblical incidents are said to be examples of Jewish ritual (e.g. Baptism as ritual cleansing, and the Last Supper as a passover seder). However, these practices are also present in several non-Christian, non-Jewish, ancient religions, a fact that made several church fathers uncomfortable. So similar were the practices of major rivals, such as Mithraism, and so obviously did they occur before the existence of Christianity, and unconnected to Judaism, that church fathers such as Tertullian and Justin Martyr argued that Satan himself had given the rituals to the rival religions, as a sort-of prophetic mockery. According to several secular scholars, the fact that even early Christian church fathers admitted that the other religions used these rituals, and that they admitted the other religions used them first, suggests that Christianity adopted them from these sources, and the biblical narrative was invented later to justify Christian usage. However, it could also be argued that the biblical narrative refers to the practices as they were known in Judaism, while the forms in traditional Christianity were taken from other religious sources.
The Council of Jerusalem, according to Acts 15, determined that circumcision was not required of Gentile converts, only avoidance of "pollution of idols, fornication, things strangled, and blood" (KJV, Acts 15:20), establishing nascent Christianity as an attractive alternative to Judaism for prospective Proselytes. The Twelve Apostles and the Apostolic Fathers initiated the process of integration of the originally Jewish sect (outlawed as religio illicita since the 80s) into Hellenistic religion (Christianity and Neoplatonism), a process culminating only at the end of Classical Antiquity, with Pseudo-Dionysius the Areopagite.
The Armenian and Ethiopian churches are the only instances of imposition of Christianity by sovereign rulers predating the council of Nicaea. The initial conversion of the Roman Empire occurred mostly in urban areas of Europe, where the first converts occurred through the conversion of most of the Jewish population. Later conversions happened among the Grecian-Roman-Celtic populations over centuries, again mostly among its urban population and only spread to rural populations in much later centuries. The term "pagan" is from Latin, it means "villager, rustic, civilian" and is derived from this historical transition. The root of that word is present in today's word "paisan" or "paisano". Consequently, while the initial converts were found among the Jewish populations, the development of the Orthodox Church as an aspect of State society occurred through the co-option of State Religion into the ethos of Christianity and only then was conversion of the large rural population accomplished.
See main article: Constantine I and Christianity.
When Yale historian Ramsay MacMullen treated the Christianization of the Roman Empire, he divided his book in two sections, before and after the year 312, which marked the momentous conversion of Constantine. Constantine ended the persecution of Christianity (and other religions) with the Edict of Milan, so that the Imperial pagan religion of Ancient Rome was no longer the only acceptable religion by the state. Whether or not Constantine himself was a proponent of what was to follow is contested. Under Constantine's successors, Christianization of Roman society proceeded by fits and starts, as John Curran recently documented in detail.
Constantine's sons, for example, banned pagan State religious sacrifices in 341, but did not close the temples. Although all State temples in all cities were ordered shut in 356, there is evidence that traditional sacrifices continued. Under Julian, the temples were reopened and State religious sacrifices legalized once more. When Gratian declined the position and title of Pontifex Maximus, his act effectively brought an end to the state religion due to the positions authority and ties within the Imperial administration. Again however, this process ended State official practices but not the private religious practices. Consequently, the temples remained open until Theodosius I made the public expression of the ancient cults illegal, bringing an era of religious toleration decisively to an end.
After Rome was declared a Christian Empire by Theodosius in 380, laws were passed against pagan practices over the course of the following years. Many of the ancient pagan temples were subsequently defiled, sacked, and destroyed, or converted into Christian sites. As such, the Christianization attributed to Constantine eventually became a more coercive process under Theodosius.
The early Christianization of the various Germanic peoples was achieved by various means, and was partly facilitated by the prestige of the Christian Roman Empire amongst European pagans. The early rise of Germanic Christianity was, thus, mainly due to voluntary conversion on a small scale.
In the 4th century some Eastern Germanic tribes, notably the Goths, an East Germanic tribe, adopted Arianism. From the 6th century, Germanic tribes were converted (and re-converted) by missionaries of the Roman Catholic Church, firstly among the Franks, after Clovis I's conversion to Catholicism in 496. The Lombards adopted Catholicism as they entered Italy, also during the 6th century.
Unlike the history of Christianity in the Roman Empire, conversion of the West and East Germanic tribes took place "top to bottom", in the sense that missionaries aimed at converting Germanic nobility first, which would then impose their new faith on the general population.
The Franks were converted in the 5th century, after Clovis I's conversion to Catholicism. In 498 (497 or 499 are also possible) he let himself be baptised in Reims. With this act, the Frankish Kingdom became Christian, although it would take until the 7th century for the population to abandon some of their pagan customs. This was typical of the Christianization of Europe. Christian and pagan practices would effectively exist in parallel.
See also: Anglo-Saxon Christianity and Hiberno-Scottish mission. During the reign of Ethelbert of Kent, Pope Gregory I decided to regain the island for Christianity. Between the sixth and the tenth century, the mission of the Catholic Church and the Hiberno-Scottish mission Christianized England, working largely independently.
See main article: Germanic Christianity. The Germanic peoples underwent gradual Christianization in the course of the Early Middle Ages, resulting in a unique form of Christianity known as Germanic Christianity in some cases. The Eastern and Western tribes were the first to convert through various means. However, it wouldn't be until the 12th century until the North Germanic Tribes had Christianized.
In the polytheistic Germanic tradition it was even possible to worship Jesus next to the native gods like Wodan and Thor. Before a battle, a pagan military leader might pray to Jesus for victory, instead of Odin, if he expected more help from the Christian God. Clovis had done that before a battle against one of the kings of the Alamanni, and had thus attributed his victory to Jesus. Such utilitarian thoughts were the basis of most conversions of rulers during this period. The Christianization of the Franks lay the foundation for the further Christianization of the Germanic peoples.
See main article: Anglo-Saxon mission. The next impulse came from the edge of Europe. Although Ireland had never been part of the Roman Empire, Christianity had come there and developed, largely independently into Celtic Christianity. The Irish monks had developed a concept of peregrinatio. This essentially meant, that a monk would leave the monastery and his Christian country to proselytize among the heathens, as self-chosen punishment for his sins. From 590 onwards Irish missionaries were active in Gaul, Scotland, Wales and England.
On the Continent, the West Germanic Saxon peoples were converted by force. In the course of the Saxon Wars Charlemagne destroyed their Irminsul in 772, and in 782 he allegedly ordered the beheading of 4,500 Saxon nobles who were caught practicing their native paganism in spite of being baptized, at the Blood court of Verden.
See main article: Christianization of Bulgaria. After its establishment under Krum of Bulgaria, the new Kingdom of Bulgaria found itself between the kingdom of the East Franks and the Byzantine Empire. Christianization then took place in the 9th century under Boris I of Bulgaria. The Bulgarians became Eastern Orthodox Christians and the Bulgarian Orthodox Church was created.
See main article: Christianization of Poland.
See also: Pagan reaction in Poland.
The "Baptism of Poland" (Polish: Chrzest Polski) in 966 refers to the baptism of Mieszko I, the first ruler of a united Polish state. His baptism was followed by the building of churches and the establishment of an ecclesiastical hierarchy. Mieszko saw baptism as a way of strengthening his hold on power, with the active support he could expect from the bishops, as well as a unifying force for the Polish people. Mieszko's action proved highly successful; by the 13th century, Roman Catholicism had become the dominant religion in Poland.
See main article: Christianization of Kievan Rus'. Between the 8th and the 13th century the area of what now is Belarus, Russia and the Ukraine was settled by the Kievan Rus'. An attempt to Christianize them had already been made in the 9th century, with the Christianization of the Rus' Khaganate. The efforts were finally successful in the 10th century, when about 980 Vladimir the Great was baptized at Chersonesos.
See main article: Christianization of Scandinavia. For the purposes of this article the Christianization of Scandinavia refers to the process of conversion to Christianity of the Scandinavian people, starting in the 8th century with the arrival of missionaries in Denmark and it was at least nominally complete by the 12th century, although the Samis remained unconverted until the 18th century.
In fact, although the Scandinavians became nominally Christian, it would take considerably longer for actual Christian beliefs to establish themselves among the people. The old indigenous traditions that had provided security and structure since time immemorial were challenged by ideas that were unfamiliar, such as original sin, the Immaculate Conception, the Trinity and so forth. Archaeological excavations of burial sites on the island of Lovön near modern-day Stockholm have shown that the actual Christianization of the people was very slow and took at least 150-200 years, and this was a very central location in the Swedish kingdom. 13th century runic inscriptions from the bustling merchant town of Bergen in Norway show little Christian influence, and one of them appeals to a Valkyrie. At this time, enough knowledge of Norse mythology remained to be preserved in sources such as the Eddas in Iceland.
See main article: Northern Crusades. The Northern Crusades or Baltic Crusades were crusades undertaken by the Catholic kings of Denmark and Sweden, the German Livonian and Teutonic military orders, and their allies against the pagan peoples of Northern Europe around the southern and eastern shores of the Baltic Sea. Swedish and German campaigns against Russian Eastern Orthodox Christians are also sometimes considered part of the Northern Crusades.  Some of these wars were called crusades during the Middle Ages, but others, including most of the Swedish ones, were first dubbed crusades by 19th century romantic nationalist historians.
See main article: Christianization of Lithuania. Lithuania and Samogitia were ultimately Christianized from 1386 until 1417 by the initiative of the Grand Duke of Lithuania Jogaila and his cousin Vytautas.
See main article: Reconquista. Between 711–718 the Iberian peninsula had been conquered by Muslims in the Umayyad conquest of Hispania; Between 722 (see: Battle of Covadonga) and 1492 (see: the Conquest of Granada) the Christian Kingdoms that later would become Spain and Portugal reconquered it from the Moorish states of Al-Ándalus. The notorious Spanish Inquisition and Portuguese Inquisition were not installed until 1478 and 1536 when the Reconquista was already (mostly) completed.
The expansion of the Catholic Portuguese Empire and Spanish Empire with a significant roled played by the Roman Catholic Church led to the Christianization of the indigenous populations of the Americas such as the Aztecs and Incas. Later waves of colonial expansion such as the Scramble for Africa or the struggle for India, by the Dutch, England, France, Germany and Russia led to Christianization of other native populations across the globe such as the American Indians, Filipinos, Indians and Africans led to the expansion of Christianity eclipsing that of the Roman period and making it a truly global religion.