Nontrinitarianism (or antitrinitarianism) refers to monotheistic belief systems, primarily within Christianity, which reject the mainstream Christian doctrine of the Trinity, namely, the teaching that God is three distinct hypostases or persons who are coeternal, coequal, and indivisibly united in one being or ousia.According to churches that consider ecumenical council decisions final, trinitarianism was definitively declared to be Christian doctrine at the 4th-century ecumenical councils, that of the First Council of Nicaea (325), which declared the full divinity of the Son, and the First Council of Constantinople (381), which declared the divinity of the Holy Spirit.Some councils later than that of Nicaea but earlier than that of Constantinople, such as the Council of Rimini (359), which has been described as "the crowning victory of Arianism", disagreed with the Trinitarian formula of the Council of Nicaea.