Columbia subject headings:
Apologetics--Early works to 1800.
Apologetics--History--Early church, ca. 30-600.
Harvard subject headings:
Apologetics--Early works to 1800
Apologetics--History--Early church, ca. 30-600
Princeton subject headings:
Apologetics--Early works to 1800.
Apologetics--History--Early church, ca. 30-600.