The Council of Nicaea

There never was a church council that decided this. The council of Trent in the middle of the 16th century is the first big council that actually made a decision. Most people today, at least in our generation, can get a lot of their understanding of Christian history from Dan Brown's book "The Da Vinci Coates" I tell my students, look, if you want to know about the history of the Middle Ages, don't do it by watching Monty Python and the Holy Grail.