Columbia subject headings:
Harvard subject headings:
Apostolic Fathers.
Barnabas, Apostle, Saint.
Christian literature, Early.
Christian martyrs.
Clement I, Pope.
Hermas, active 2nd century.
Ignatius, Saint, Bishop of Antioch, -approximately 110
Polycarp, Saint, Bishop of Smyrna.
Theology
Princeton subject headings:
Theology--Early works to 1800.