Columbia subject headings:
Civilization, Medieval--Congresses.
Work--History--Congresses.
Working class--History--Congresses.
Harvard subject headings:
Civilization, Medieval--Congresses
Philosophy, Medieval--Sources.
Work--Congresses
Work--History--Congresses.
Work--Religious aspects--Christianity--Sources.
Princeton subject headings:
Civilization, Medieval--Congresses.
Work--History--Congresses.
Working class--History--Congresses.