How western Europe became Christian

Christianity began in the 1st century as a small religious community within the Roman Empire. It spread gradually despite periods of persecution.

In the early 4th century, a major turning point came when Emperor Constantine the Great ended the persecution of Christians.

In 313, the Edict of Milan granted freedom of worship throughout the empire and restored confiscated church property.

As a result, this proclamation effectively established religious toleration for Christianity and allowed the institutional Church to openly organize.

Constantine himself, who was converted to Christianity, became its patron. He convened the First Council of Nicaea in 325, where bishops from across the empire defined core Christian beliefs in the Nicene Creed.

This helped unify Christian doctrine across Western and Eastern regions. 

By the end of the 4th century, Christianity had moved from tolerance to dominance.

In 380, Emperor Theodosius I declared Nicene Christianity the official state religion of the Roman Empire.

He enforced the faith with imperial authority, threatening punishment for those who followed unorthodox core beliefs.

Over the next decade, Theodosius issued decrees that shut down pagan temples and banned traditional polytheistic rituals.

The old Greco-Roman pagan religion was increasingly suppressed, and public pagan worship largely disappeared.

By 391, temple doors were closed and pagan sacrifices were forbidden, completing the empire’s religious conversion to a Christian realm.

Consequently, this era saw a cultural shift as Christian orthodox practices and values permeated Roman society.

The once-persecuted sect had now become the spiritual basis of European civilisation. 

In the Western Empire, political structures were collapsing under barbarian invasions during the 5th century, but the institutional Church remained intact.

When the Western Roman Empire fell in 476, the Catholic institutional Church, as the Western institutional Church came to be known, became a source of continuity and authority.

During this time, many barbarian peoples who had settled in Europe began to convert to Christianity.

Several Germanic tribes had already adopted a form of Christianity before entering the empire, though most followed the Arian doctrine (a non-orthodox theology) rather than the Nicene Creed. 

In the late 5th century, a landmark religious conversion in Western Europe was that of Clovis I, king of the Franks.

According to tradition, Clovis converted to Catholic (Nicene) Christianity around 496 after he won a crucial battle.

He was baptised in Reims, and this won him the active support of the Gallo-Roman Catholic clergy.

The Franks’ religious conversion was significant because Clovis and his successors championed Catholic Christianity rather than Arianism, aligning themselves with the papacy and the older Roman Christian population.

Over the next century, the other Germanic kingdoms in the West followed suit. In Spain, the Visigoths renounced Arianism under King Reccared, who converted to Catholic Christianity in 587.

Not long after, in 589, the Third Council of Toledo affirmed the Visigothic kingdom’s Catholic faith.

In Italy, the Lombards had been Arian Christians, but by the end of the 7th century they too had accepted Catholicism.

So, by AD 600 most of Western Europe’s post-Roman kingdoms were officially Christian. 

While Christianity survived in continental Europe, it also found a strong foothold in the British Isles.

Roman Britain had a Christian presence by the 4th century, but the collapse of Roman rule in Britain (early 5th century) and the arrival of pagan Anglo-Saxon tribes meant that the faith needed to be replanted.

Missionary efforts from two directions converged on the British Isles. From the west, Irish Christianity flourished after St. Patrick’s mission in the 5th century.

Patrick, who was a Romano-British missionary, began converting Ireland around 432.

Ireland became a largely Christian land and developed its own monastic culture.

Irish monks, in turn, embarked on missionary journeys to Scotland and continental Europe.

For example, the Irish abbot Columba founded the monastery of Iona , located on the Scottish coast, in 563, which became a base for converting the Picts in Scotland.

Irish Christian missionaries such as Saint Columbanus later travelled to the Frankish realms in the 6th and 7th centuries, founding religious monasteries in Gaul and Italy and reinvigorating Christian practice in places where it had declined. 

From the south, the Roman institutional Church sent Christian missionaries to the pagan Anglo-Saxon kingdoms of Britain.

In 597, Pope Gregory I, known as Gregory the Great, dispatched a missionary party led by Augustine of Canterbury to the Kingdom of Kent in England.

King Æthelberht of Kent and many of his nobles accepted Christianity, partly due to the influence of Æthelberht’s Frankish Christian wife, Queen Bertha.

Æthelberht’s baptism opened the way for the religious conversion of his people.

Augustine became the first Archbishop of Canterbury and established the English institutional Church hierarchy with papal support.

The religious conversion of England proceeded kingdom by kingdom. Missionaries usually sought the religious conversion of the local king first; once a ruler was baptised, his subjects often followed their leader’s faith.

This top-down approach is illustrated by the case of King Rædwald of East Anglia, who accepted Christianity but kept a pagan altar alongside a Christian one, indicating a transitional period of dual practice.

Over the 7th century, all the Anglo-Saxon realms gradually became Christian. The last pagan Anglo-Saxon ruler, King Arwald of the Isle of Wight, was defeated in 686. 

By the 8th century, the Frankish Kingdom (in modern France and Germany) had emerged as the dominant power in Western Europe, and it became a main contributor in Christianisation.

The Frankish rulers, especially from the Carolingian dynasty, formed a close alliance with the institutional Church.

Pepin the Short became King of the Franks in 751 and, with papal approval, granted the Pope territory in Italy in 756.

This was known as the Donation of Pepin and it would lay the foundation for the future Papal States.

As evidence of this, it demonstrated the growing church–state relations in the West, where kings protected and endowed the institutional Church, and the institutional Church legitimized kings. 

Frankish support was crucial in a new wave of missionary activity on the European continent.

Saint Boniface, who was an English missionary, received backing from Pepin and his successor Charlemagne to evangelise the Germanic tribes beyond the Rhine.

Boniface travelled in the early 8th century to regions such as Frisia, Thuringia, and Hesse, which are located in present-day Germany.

He founded churches and religious monasteries and was eventually made a bishop.

With Frankish military and political support, Christian missionaries like Boniface were able to convert many Germanic communities that had remained pagan.

The Bavarians, Thuringians, Frisians, and others were gradually brought into the Christian fold during this period.  

Charlemagne, who ruled as King of the Franks from 768 and later as Emperor, aggressively expanded Christian rule.

He saw it as his duty to spread the faith, often by force. His most notable campaign was against the Saxons, a pagan Germanic people in what is now northern Germany.

The Saxons resisted Frankish rule and Christian missionaries for decades. Charlemagne fought the Saxon Wars to subdue them.

After each rebellion, he imposed harsh measures to ensure religious conversion. In 782, after a major Saxon uprising, Charlemagne ordered the Massacre of Verden, executing thousands of captured Saxon warriors who had refused baptism.

These brutal tactics shocked even some of Charlemagne’s contemporaries. The scholar Alcuin urged the king to evangelise more patiently, but the tactics eventually broke Saxon resistance.

By the end of Charlemagne’s reign, the Saxons were nominally Christian and integrated into his empire. 

On Christmas Day in the year 800, Pope Leo III crowned Charlemagne as Emperor of the Romans in Rome.

This act revived the idea of a Western Roman Empire and established the Holy Roman Empire, linking the concept of empire with Christian leadership.

The coronation showed a strong connection between the Latin institutional Church and Western secular authority: the Pope conferred legitimacy on the emperor, and the emperor in turn protected the institutional Church.  

By the 10th century, most of Central Europe had been Christianised, and attention turned to the Scandinavian north and the edges of the continent.

The Vikings of Scandinavia had been infamous as pagan raiders during the 8th and 9th centuries, even attacking Christian religious monasteries.

In the 10th century, however, the Viking homelands began to accept Christianity.

Denmark was the first Scandinavian kingdom to officially convert. King Harald Bluetooth of Denmark was baptised around the year 965.

According to legend, a missionary named Poppo proved the power of the Christian God by holding a red-hot iron without being burned, convincing Harald to convert.

While Harald’s declaration brought Christianity to Denmark’s royalty, the common people converted more gradually.

Many Danes remained pagan into the late 10th century, and it took further efforts by English Christian missionaries (and pressure from Christian kings like Canute in the 11th century) to complete the religious conversion. 

In Norway, religious conversion was driven by its kings, often by force. Olaf Tryggvason, who ruled Norway in the late 10th century, had become Christian while raiding in England.

Upon taking power, he and later Olaf II Haraldsson, worked to establish Christianity throughout Norway.

They faced resistance from pagan chieftains, and violent conflicts erupted. Olaf II, in particular, is credited with consolidating Christianity in Norway, though he died in battle against pagan rebels.

Within a few decades of his death, Norway firmly identified as a Christian kingdom, and Olaf II was revered as a martyr and saint.

In the Norwegian outposts of the North Atlantic, religious conversion also took hold.

Iceland’s parliament, the Althing, voted in the year 1000 to adopt Christianity as the law of the land, which avoided conflict by making a collective decision to baptise the population and allowed some pagan customs to fade out gradually.

Similarly, Greenland, which was settled by Norse colonists, saw bishops appointed by the 11th century. 

Sweden was the last of the Scandinavian realms to Christianise fully. Missionaries had made inroads among the Swedes earlier, such as the missionary Ansgar who visited in the 9th century, but widespread religious conversion came slowly.

By the mid-11th century, there were Christian kings in Sweden, but pagan worship still lingered.

In fact, the temple at Uppsala, where Norse gods were worshipped, continued to operate into the early 1100s.

Eventually, the old sanctuary was closed and Sweden became officially Christian. 

Central Europe also saw its final pagan rulers convert during the 10th century. The Polish Duke Mieszko I, who was baptised in 966.

His decision was influenced by his marriage to a Czech princess, Dobrawa, and by the political need to ally with Christian neighbors.

Embracing Catholic Christianity protected Poland from potential conquest by German rulers, who might otherwise claim a right to subjugate pagan lands.

Mieszko’s baptism is considered the founding moment of the Polish state in European history.

He established a Latin-rite church hierarchy in his realm, linking Poland firmly to Western Christendom.

Similarly, in the Kingdom of Hungary, Prince Géza and his son Stephen accepted Christianity in the late 10th century.

Stephen, who was originally Vajk, was baptised and devoted himself to making Hungary a Christian kingdom.

On Christmas Day in the year 1000, Stephen I was anointed as the first King of Hungary, reportedly receiving a crown from Pope Sylvester II as a symbol of papal recognition.

He organised dioceses, founded churches and religious monasteries, and made the Catholic faith the foundation of his state.

For his role in converting his country, Stephen was later canonised a saint. By the early 11th century, Poland, Hungary, and the Scandinavian kingdoms had all joined the Christian world.

This meant that virtually all of Europe, from Ireland and England in the west to the Slavic lands in the east, from Scandinavia in the north to the Mediterranean in the south, was under Christian influence.

Pagan religions survived only in isolated pockets.