What heresy was condemned at the Council of Ephesus?

The Council of Ephesus, which took place in 431 AD, primarily condemned Nestorianism. This heresy was associated with the teachings of Nestorius, the Bishop of Constantinople, who proposed a distinct separation between the divine and human natures of Christ. He suggested that Mary should not be referred to as Theotokos, or "Mother of God," since he believed she only gave birth to the human aspect of Christ, rather than the divine.

The council affirmed the unity of Christ's two natures—divine and human—asserting that both natures coexisted in one person. The affirmation of Mary as Theotokos was a critical point, emphasizing the belief in Christ's dual nature and his divinity. By condemning Nestorianism, the council aimed to uphold this integral doctrine of Christology within the framework of Christian belief.

The other heresies mentioned, while significant in their own contexts, were not the primary focus of the Council of Ephesus. Docetism, which denied the reality of Christ's humanity, Monophysitism, which posited that Christ's nature was solely divine, and Arianism, which denied the full divinity of Christ, were addressed in other councils