During the 4th and 5th centuries, heresies and controversies started popping up in the Church. Donatism was an early deviation that was started by the Bishop of Carthage, who stated that the validity of the sacrament was based on the priest giving it, while Montanism proclaimed that there would be new prophets to warn of the Second Coming of Christ. One of the most sinister heresies was Arianism. Starting around the year 300, the Alexandrian Presbyter Arius preached that Christ was not equal to the Father and that the Son was not fully God. Many emperors and bishops agreed with this doctrine and persecuted people practicing the true faith. 

Arianism was condemned in 325 at the First Council of Nicea, which also made advancements in Church governance. The Council of Constantinople in 381 dealt further with Arianism and made additions to the Nicene Creed. Another influential subversion was monophysitism, the belief that Christ only had one nature, which was divine. It was struck down at the Council of Chalcedon in 451. 

There are two main ways to practice Christian monasticism: Eremitic – monks (sometimes called hermits) live in isolation in a secluded place like a forest or desert; and Cenobitic – a group of monks who live and pray together in a monastery. St. Anthony of Egypt (250-335) left his monastery, went to be a hermit in the desert of Egypt, and asked that he be left in solitude. However, 300 people followed him and his example and also became hermits. 

By the year 300, women also started becoming monastics and are now known as nuns. St. Benedict made many of the rules followed today in Western monasteries. The main center of Western monasticism is Monte Casino and the East’s is Mount Athos. Monks also invented many agricultural techniques, wrote a large amount of books and writings, and started copying manuscripts that were used in Medieval Europe. 

Many early Christian apologists thought that the ancient Greek philosophers had a root in the Christian faith, like St. Justin Martyr. Originally a Platonist, he was converted to Christianity and preached extensively to Jews and Pagans, eventually being beheaded for his faith. 

The early heresies of the Church such as Arianism, Monophysites, and Origensim, were superseded by later problems like Iconoclasm and Muslim empires that invaded christian lands and would later cause war between the two religions in the Middle Ages. 

Following the earthly time of Jesus, Christianity first spread around the Jewish lands. The Jewish religious leaders intensely persecuted Christians, including Stephen, a deacon in Judea. After confessing his faith, Stephen was stoned to death by the Jews, including Saul of Tarsus, who would become a Christian apostle. 

Saul later traveled to the Syrian city of Damascus to arrest Christians. While Saul was on the road, he saw a vision of Jesus Christ, who told him to stop fighting Christianity and to go to Damascus and join the Christian movement there. Saul changed his name to Paul and was converted to Christianity, going on to teach that the Christian message was not only intended for Jews. Additionally, Paul preached that the Law of Moses did not need to be followed anymore because it had already been fulfilled by Christ. Paul traveled more than 13,000 miles until he was beheaded in Rome because of his faith. 

The emperor Nero was one of the first rulers of Rome to start an empire-wide persecution of Christians, who he blamed for the suffering during his reign. The emperors Domitian and Diocletian also fervently fought against the Christian faith. 

During the 3rd Century, many Romans in the cities stopped practicing the traditional pagan religion, which was still only widely followed in the countryside. Christianity was not officially outlawed until 250, after the reign of Nero. During a three-year span under the emperor Diocleitan known as the “Great Persecution,” thousands of Christians were tortured and killed for their faith. At the Battle of Milvian Bridge in 312, the emperor Constantine was converted to Christianity after seeing a vision of a cross in the sky. Constantine later legalized Christianity by the Edict of Milan in 313. 

Didache wrote down the teachings of the Twelve Apostles. These works weren’t rediscovered until 1873. Clement of Rome, Ignatius of Antioch, and Polycarp were notable Christian writers. All were martyred in 107. The Apologists were a group of Christians who defended the Church against heresy and persecution with logic and reason. 

Since the Empire had become Christian, bishops of the Church started having power over the emperor. Theodosius, the emperor after Constantine, was not allowed into the Church by Bishop Ambrose because he slaughtered 3,000 rebels who had already surrendered. 

Before the 11th Century, all of the main Bishops were first among equals, until the Western Church tried to get more power for the Bishop of Rome. This caused the Great Schism in 1054 between the Western Catholic Church and the Eastern Orthodox Church.