Final answer:
St. Augustine played a pivotal role in settling the Donatist controversy at the 411 Council of Carthage, leading to the expulsion of the Donatists from the church, and his contributions to Christian doctrine and medieval philosophy were profound.
Step-by-step explanation:
St. Augustine, as the Bishop of Hippo, was instrumental in resolving the Donatist controversy during the early centuries of Christianity. The controversy centered on the legitimacy of sacraments performed by clergy who had renounced their faith under persecution, leading to a schism in the North African Christian community. At the 411 Council of Carthage, convened by the emperor to address this issue, Augustine argued against the Donatist view, which ultimately led to the expulsion of the Donatists from the church. Although the Donatist sect persisted for some time, Augustine's efforts at the council were a decisive moment in the controversy.
In the broader scope of his work, Augustine also fought against various heresies and was a prolific writer on Christian doctrine. His influential work The City of God offered reassurance to Christians after the Visigoths' sack of Rome and outlined a vision of a Christian society that would endure beyond earthly kingdoms. This and his many other writings left a lasting impact on both the church and medieval European philosophy.