AD 300 – 1000
What was happening during this period?
This was a time of unrest in the Church. There were several heresies gaining popularity and against Church teachings and doing damage to the believers. They needed to be corrected. Some are listed below.
The Church called for councils to respond to heresies and to define the teachings. This is a time when saints made a big impact on the course of history and the Church. They wrote, influenced or helped to define the truth. They helped steer the Church and world in the right direction.
Heresy is the holding and spreading of beliefs that go against accepted church teaching.
| Time | Heresy | False teaching | Church action | Saints |
| 320 – 600 | Arianism | Denied the divinity of Christ – Jesus | Council of Nicaea | Saint Athanasius |
| Fifth Century | Pelagianism | Denied the necessity of Grace and denied original sin | Council of Carthage | St Augustine Pope St Gregory the Great |
| 431 | Nestorius | Christ is two-persons Mary is not the mother of God | St Cyril | |
| seventh century | Monothelitism | Christ has only one nature | Pope Leo 1 the Great | |
| Eighth and ninth centuries | Iconaclasism | Destruction of sacred images | The Second Council of Nicaea AD787 | St John Damascene |
| 1054 | Byzantines Great Schism | |||
Click on each of these saints to find out more about each one.

St Athanasius 
St Augustine 
Pope St Gregory the Great 
St John Damascene 
Pope St Leo the Great 
St Cyril
