Columbia subject headings:
Citizenship--Europe--History.
Harvard subject headings:
Citizenship--Europe--History.
Princeton subject headings:
Caracalla, Emperor of Rome, 188-217--Influence--Congresses.
Citizenship--Europe--History--19th century--Congresses.
Citizenship--Political aspects--Rome--History--Congresses.
Citizenship--Social aspects--Rome--History--Congresses.
Constitutio Antoniniana--Congresses.