Columbia subject headings:
Christianity--Rome--Congresses.
Church and state--History.
Church history--4th century--Congresses.
Church history--4th century.
Harvard subject headings:
Christianity--Rome.
Church and state--History
Church history--4th century.
Church history--Primitive and early church, ca. 30-600
Princeton subject headings:
Chritianity--Rome--Congresses.
Church history--4th century--Congresses.
Constantius II, Emperor of Rome, 317-361--Congresses.