The Coptic Apocalypse of Peter: Nag-Hammadi-Codex VII,3

As an accompaniment to the corpus of the Griechischen Christlichen Schriftsteller (GCS), Adolf von Harnack created the monograph series Texte und Untersuchungen zur Geschichte der altchristlichen Literatur (TU) in 1882, which from that time on served as an "archive for the ... editions of older Christian writers".