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The Reign of Constantine the Great

God finally put an end to the terrible Roman persecutions when Constantine the Great (A.D. 307–337) became Emperor of Rome. The story of how he converted to Christianity is interesting. Before his conversion to Christianity, this Emperor was at war with Maxentius. Seeing that Maxentius’ army was superior to his, Constantine prayed to God for assistance. A bright cross appeared in the sky with an inscription that says, “In this sign, thou shalt conquer.” Therefore, Constantine ordered that a banner be made with the sign of the cross on it, and he commanded his soldiers to carry it in battle. Under the banner of the cross, he defeated the forces of Maxentius in the famous battle at the Milvian Bridge. He attributed his victory to the Christian God. Since then (A.D. 312), he has become a staunch defender and protector of Christianity.

During his rule, Constantine practiced religious tolerance, and by the Edict of Milan (A.D. 313), he granted Christians the opportunity to practice their religion freely. He even built beautiful churches for them and showed priests, bishops, and the popes great honor and distinction. His mother, St. Helena, also became a Christian and used her wealth to visit those places in Palestine that were memorable to our Lord. It was during one of her visits that she discovered the Holy Cross, on which Christ was crucified. Following her and her son's example, many pagans also abandoned their idols and converted to Christianity. Rome had changed from being the seat of paganism to being the center of Christianity.

Emperor Constantine the Great and His Mother, Queen Helena

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Another one of Constantine’s great accomplishments was to unify the Roman Empire, which was split into the Western and Eastern Empires during the reign of Emperor Diocletian. Constantine built an imperial residence in the city of Byzantium and called it Constantinople after his name. Constantinople is now the modern-day city of Istanbul in north-western Turkey.

Years later, the Roman Empire had been divided again following the death of Emperor Jovian in A.D. 364. Emperor Valentinian ruled the Roman Empire in the west and Emperor Valens in the east. Eventually, the Eastern Roman Empire came to be known as the Byzantine Empire because its capital was Constantinople, which was the old city of Byzantium. For the division of the Roman Empire and the Church into the East and the West, see this Map. (The red line in the map indicates the approximate dividing line between the two.)

For a listing of Roman Emperors up to A.D. 491, see the Encyclopedia Brittanica.

Heresy During the Fourth, Fifth, and Sixth Centuries

While the Church enjoyed a respite from persecutions during the reign of Constantine the Great, her battle against heresy continued. It was during this time that the Church, by defending the faith against the criticisms and attacks of the heretics, was able to refine and clarify her doctrines on Christology and the Trinity.

A summary of the six major heresies during the fourth, fifth, and sixth centuries is given in the chart below:

One of the most widely held heresies that the Church had to struggle with during this time was Arianism, which denied the divinity of Christ. What made it so difficult to eradicate was that it was supported, not just by a small band of heretics but also by many well-meaning clergymen, bishops, and even Emperors and local governors. Thanks to the work of St. Athanasius (A.D. 296–373), who stood against the world—contra mundum—as a great champion of orthodoxy, the Church was saved from being completely engulfed by this heresy. Constantine the Great himself was surrounded by Arians in his court. It was through the lies and false accusations of his Arian advisers that Constantine wrongfully banished St. Athanasius from his post in Alexandria to Trier, a Roman city in northern Europe. However, Constantine himself was not an Arian, and it is not true that he was baptized and died a heretic. See Was Constantine the Great Baptized an Arian?

St. Augustine (A.D. 354–430), another Father of the Church, also contributed greatly to the fight against heresy during the fourth and fifth centuries. Although he embraced the Manichean heresy during his younger days, St. Augustine was converted by the prayers of his mother, St. Monica, and the preaching of another great saint and Father of the Church, St. Ambrose.  After his conversion, however, St. Augustine did not merely engage in theoretical disputations with various heretics (the Donatists, the Pelagians, and the Manicheans), but also went on to explain the various dogmas of revelation. He wrote extensively on God, the Holy Trinity, the role of grace, and its influence on our free will and sanctification.

Although the major heresies in the Church had already been settled and condemned by various Church Councils during this period, some of them continued to recur in various forms beyond the sixth century and up to the Protestant Reformation (1517–1648) and beyond. It is not unusual to see even today scholars whose teachings still echo the old errors of the ancient heretics in the first few centuries of the Christian era.

Progress in Holy Scripture

Due to the disruptions caused by the Roman persecutions and the doctrinal turbulence caused by heretics during the first three centuries of the Christian era, the Church’s awareness regarding the status of the sacred books did not develop quickly but only gradually. However, although the canon of the Holy Scripture was not formally defined until the Council of Trent in A.D. 1546, the Church had enunciated the correct list of inspired books as early as the fourth century. The Council of Carthage enunciated the canon in A.D. 397 (Denzinger #92).


Although Latin translations of some of the sacred books were available since the second century, St. Jerome (A.D. 347–420), at the request of Pope St. Damasus I, undertook the task of improving the existing Latin translations as well as translating the whole Old Testament from the original Hebrew and Greek into Latin. His translation replaced all previous Latin translations of the Bible and became the only Latin Bible in the Western Church until the Council of Trent. Because it was widely used, it was appropriately called the Vulgate Bible (from the Latin vulgata, which means “disseminated”).

The Rise of Monasticism


Besides the progress made by the Fathers in combating heresy and the progress of the Church in the development of the Canon of the Holy Scriptures, the rise of monasticism and religious orders in the fourth century was another important development that would have a profound effect on the future life of the Church. Some monks lived in the deserts of Egypt and Palestine even during the third century, but they usually lived alone and served God in solitude. In the fourth century, however, Saint Anthony the Great, aka St. Anthony of Egypt (A.D. 251–356) began bringing monks together to live in communities instead of in isolation. He drew up a rule of life for his new monks, which included making vows of poverty, chastity, and obedience.


The monks spent their time fasting, praying, and laboring. Although they lived together in small monasteries, each of the monks had his room or cell where he prayed and performed works of penance. Although the monks were often bound by vows of poverty, chastity, and obedience, most of them (unlike many present-day monks) were not ordained priests or deacons. Soon, monasteries and monastic life spread outside Egypt and throughout the Christian world. Saint Augustine brought monasticism to Africa and even organized communities of female religious, for whom he also drew up Rules. However, monasticism came close to perfection with St. Benedict of Nursia (A.D. 480–543), who built a monastery at Monte Cassino in A.D. 530. His now famous Rule of St. Benedict is remarkable for its moderation and has become the template that other religious orders followed.

Saint Benedict of Nursia writing the Benedictine Rule

Portrait in the Church of  Heiligenkreuz Abbey, Lower Austria

Painted by Herman Nieg (1849-1928)

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The spirit of St. Benedict’s rule is summarized in the Benedictine motto: ora et labora (“pray and work”). However, St. Benedict widened the concept of work to include not merely manual labor but also intellectual labor. Henceforth, the monks had been busy, not merely in various forms of trade and agriculture but also in teaching and other intellectual pursuits. One of their best contributions to the Church (and to the world!) in this regard was the preservation of the literature and history of the ancient world. During the Barbarian Invasions and through the Middle Ages, they painstakingly copied and preserved the works of the great Greek and Latin writers. They also devoted much of their time to diligently copying the books of the Holy Scriptures, an effort that they continued until the invention of the printing press in 1450. Without the dedication and industry of these Benedictine monks, much of the legacy handed on by the ancient world would have been lost.

The Barbarian Invasions

The Roman Empire, which had persecuted the Church for three centuries, was now about to be punished. As it had been pampered by luxury and pride, its greed and moral corruption had taken a heavy toll on its financial and military might. In the fifth century, several Germanic and Asian tribes from the north came and swept territories or provinces of the Empire. The tribes involved here were the Huns, the German Goths (both the Visigoths and the Ostrogoths), the Vandals, the Lombards, the Angles and the Saxons, and the Franks.

This point in time, when the Roman Empire was invaded by fierce tribes from the north, is known in world history as the migration of the nations, although the migrants here were not nations but nomadic tribes or barbarians. Although these people were referred to as “barbarians” in many history books, they were not complete savages. Many of them respected women and had high ideals of loyalty and devotion to their tribes. They also possessed a certain degree of agricultural and hunting skills and culture, although not as advanced as those of the Greeks or the Romans. However, they were also noted for their fierceness and violence, which was probably how they got the reputation of being “barbarians.”

In A.D. 376, the ferocious Huns from the east swept across Western Europe, driving Germanic tribes who happened to be on their way to retreat into the territories of the Roman Empire. The Huns were Mongolian migrants from Russia or central Asia. They were ruthless marauders and caused havoc wherever they went.

The retreating Visigoths, who used to live on the outskirts of the Roman Empire, at first got permission from Emperor Valens to take refuge in the Empire, but the mean attitude of Roman officials eventually caused the Visigoths to fight back. In A.D. 378, the Visigoths fought the forces of Emperor Valens at Adrianople (now known as Romania) and won. From there, they moved westward and also conquered Athens and Corinth. In A.D. 410, the Visigoths, led by Alaric I, invaded Italy, sacked Rome, and finally settled in France and Spain. Meanwhile, the Huns continued to ravage Europe. In A.D. 451, Attila, King of the Huns, who was also later known as the “Scourge of God,” was about to attack and pillage Rome when Pope St. Leo the Great negotiated a deal with him not to invade the city. Attila died in A.D. 453, and with his death, the threat from the ferocious Huns also ended.

Map of the Barbarian Invasions

by MapMaster

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Simultaneously with the movement of the Visigoths, another Germanic tribe, the Vandals, invaded other parts of the Roman Empire, particularly France and Spain. They even crossed the Straights of Gibraltar to go straight to Africa and establish their capital in Carthage. In A.D. 455, under the leadership of Geiseric, they crossed the Mediterranean, went up the Tiber River, and entered Rome. There they were again met by Pope St. Leo the Great, who pleaded not to destroy the buildings and slaughter their inhabitants. Geiseric granted the Pope’s request but took possession of its art treasures. Ginseric died in A.D. 477, but his kingdom in Carthage lasted until A.D. 534, when it was defeated by Belisarius, a general of the Byzantine Emperor Justinian (A.D. 527–565).

The Ostrogoths, a Germanic tribe that used to live near the Black Sea, occupied the areas left by the Visigoths when they fled from the Huns in A.D. 376. In A.D. 380, many of them also migrated into the Roman territories and had since been cooperating at different times with both the Visigoths and the Romans. They crossed the Danube River and proceeded to northern Italy, where they settled. In A.D. 476, Odoacer, a Visigoth chieftain, came to Rome and deposed Romulus Augustulus (the last of the Western Roman Emperors) and proclaimed himself King of Italy. This event marked the end of the Western Roman Empire. Although the Western Roman Empire had fallen, the Eastern Roman Empire (or the Byzantine Empire) continued to exist for another thousand years until it fell to the Ottoman Turks in 1453.

Now, although Odoacer claimed to recognize the supremacy of the Byzantine Emperor, the Emperor felt that the Visigoth king was rendering nothing more than lip service. In A.D. 489, he ordered an Ostrogoth leader, Theodoric, to expel Odoacer and the Visigoths from Rome. Theodoric carried out his commission, killed Odoacer, and ruled Italy until he died in A.D. 526. After his death, the succeeding Ostrogoth kings became defiant of the Byzantine Emperor, who tried to gain control of most of Italy. When Ostrogoth Totila became the new king, he recovered these Italian territories, including Rome, which he plundered. In A.D. 562, Emperor Justinian renewed his efforts toward supremacy, defeated Totila and Teia (the last Ostrogoth king) in battle, and, by further extinguishing all pockets of resistance, regained control of the whole country.

The Lombards were the last of the barbarian tribes to confront the Byzantine Emperor. After the death of Emperor Justinian in A.D. 565, they took control of northern Italy. They would like to control the entire country, but Pope St. Gregory the Great (A.D. 590–604), through his diplomatic skills, negotiated to pay them a yearly tribute to keep them from pillaging Rome.  This state of affairs continued until A.D. 754 when the Lombards lost their power to the Frankish King Pepin (father of Charlemagne), who re-conquered twenty-two towns from the Lombards and donated them to Pope Stephen II.

Just like the Visigoths, the Angles and the Saxons, who used to live in Denmark and northwestern Germany, were forced to leave their lands when the Huns were pushing westward. The Angles and the Saxons invaded Britain and fought with the Celts, the native inhabitants of Britain, where they established seven new kingdoms. Likewise, the Franks, who used to live on the east side of the Rhine River, crossed the river to escape the merciless Huns and went into Gaul, which is now called France (a name taken after the tribes who migrated there).

The political landscape of Europe changed drastically at the end of the sixth century. The Byzantine Emperor still had control of the area around Constantinople, but not much of the rest of the Western world. There was a Lombard kingdom in northern Italy, a Frankish kingdom in Gaul (or France), a Gothic kingdom in Spain (where the Visigoths settled), and seven Anglo-Saxon kingdoms in Britain. The religious landscape changed, too. Although the Church triumphed over major heresies during this period, she suffered severe losses. Many churches and monasteries were ruined, libraries burned, priests and bishops killed, and incalculable damage was inflicted on Christendom. But, on the good side, the “barbarian nations” presented themselves as fresh candidates for a new evangelization, unspoiled and uncontaminated by the moral defects of the ancient Roman civilization. The Church now had a new mission and a new world to win for Christ.

The Conversion of France

Some barbarians from the east, such as the Visigoths, were Arian Christians, but not the Franks. The Franks who went to France were entirely pagan. In A.D. 493, their king, Clovis, married a pious Catholic princess named Clotilda, who often spoke to him about the Christian religion and the need to pray to Jesus in times of difficulty. In one of his numerous battles with the Germans, he found himself overwhelmed by enemy forces. Following his wife’s advice, he prayed and vowed that if Christ would grant him victory, then he would convert and be a Christian. He did win the battle, and in A.D. 496, he, together with 3000 men, was baptized by St. Remigius, the Bishop of Rheims. All of France was soon converted after that. Since then, France has remained a Catholic country.

The Conversion of Ireland and Scotland

The conversion of Ireland was largely, but not solely, due to the missionary work of Patrick of Ireland (A.D. 389–461). He is known to many as the Apostle of Ireland, although he was not Irish but British, nor was he the first missionary to go to Ireland. Popularly called “St. Patrick”—although not officially canonized by the Church—Patrick was consecrated bishop and sent to Ireland by Pope Celestine in A.D. 432. To convert Ireland to the faith, he began working with the chieftains, the lawyers, and those who had the greatest influence on the people. He knew that when they converted, others would follow. He wanted to convert the whole country but fell short of his goal on account of his death. However, his successors continued the work and eventually converted the entire country to the faith. The zealous Irish missionaries extended their work beyond Ireland and journeyed to other countries to establish monasteries in Switzerland, Germany, and other parts of Europe. Their simple lives attracted the barbarians in Western Europe, who then entered the monasteries in droves.

In A.D. 563, the Irish missionary, St. Columba (A.D. 521–579), who is known today as the Apostle of Scotland, came to Iona (a small island on the western coast of Scotland) with twelve other companions to establish a monastery and begin the Christianization of the Scots. Because he founded numerous churches and monasteries, he was sometimes called "St. Columcille" (or St. Columbkill), which means "St. Columba of the churches."

Map of the United Kingdom of Great Britain

derivative work by Offnfopt

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St. Columba at Brideis Fort

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Since some of the missionaries were scholars, they founded schools that immediately became seats of learning in the country. Students from Scotland and other parts of Europe came to study in Scotland, which came to be known as the “Isle of Saints and Scholars.” When the students returned to their homes, they preached the gospel there, which hastened the conversion not only of Scotland but also of northern and central England. 

The Conversion of England

When the Saxons invaded England and established seven new kingdoms in the country, they destroyed not merely the Roman civilization there but also drove out the Christians to Cornwall and Wales. For there were also Christians in Great Britain as early as the second century. There were British martyrs during the persecution of Diocletian.

In the year A.D. 597, Pope St. Gregory the Great planned to send Benedictine monks to England to preach there. A story is told about why Pope St. Gregory wanted to convert the pagans in England. In A.D. 575, a Benedictine monk (the future Pope St. Gregory the Great) saw some handsome young men being sold as slaves in the markets of Rome. After inquiring about them, he learned that they were Angles (Germanic pagans from England) who had come to Rome. He was so impressed by their good looks that he exclaimed in his heart, “These are not Angles but angels!” He felt so bad that such good-looking men were being lost and deprived of God’s grace, which would make them as beautiful as angels. Since that time, he has always wanted to convert the Angles in Britain. (See Venerable Bede, The Ecclesiastical History of the English Nation, Book II, Ch. 1, last two paragraphs.)

Pope Gregory commissioned forty Benedictine monks to go to England and assigned Augustine of Canterbury to lead the group. King Ethelbert of the Kingdom of Kent, under the influence of his Christian wife, readily received the missionaries and, together with several thousand other people, was baptized. From Kent, the gospel was preached and received in other kingdoms as well. When he went back to France to request more missionaries from the bishop of Arles, who was the pope’s representative in France, Augustine was ordained bishop. He returned to England with a new band of missionaries and became archbishop of Canterbury before he died in A.D. 604. 

The conversion of England to the faith occasioned the establishment of more Benedictine monasteries and the rise of monasticism in England. One of these monks was St. Bede the Venerable (A.D. 672–735). Although he wrote volumes of commentaries on the books of Holy Scripture, his most important work was the Ecclesiastical History of the English Nation. (The book was written in Latin.) Much of what the world knows today regarding the Anglo-Saxons and the early history of England comes from this book.

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