First Council of Nicaea
The first council to gather bishops from across the Christian world, convened by the emperor Constantine. It produced the creed that states the Son is “of one essence” with the Father — the vocabulary every later argument about the Trinity has to work in.
Constantine summoned bishops from across the empire to Nicaea in 325, mainly to settle whether the Son was created. The council said he was not: he is *homoousios*, of one essence, with the Father.
What the council settled was the relation of the Son to the Father, not a general theory of how one being can be three someones. That vocabulary — one *ousia*, three *hypostaseis* — was hammered out over the following fifty years and confirmed at Constantinople in 381, whose creed is the one usually called Nicene today. Every argument in this Atlas is downstream of that settlement and constrained by it.
Sources
- The creed of Nicaea (325), completed at Constantinople (381)