Columbia subject headings:
Pliny, the Younger. Correspondence.
Pliny, the Younger. Epistolae.
Roman law.
Harvard subject headings:
Latin letters--History and criticism
Letter writing, Latin--History--To 1500
Pliny, the Younger. Correspondence
Pliny, the Younger. Epistularum libri IX.
Princeton subject headings:
Pliny, the Younger--Correspondence--Commentaries.