Even though he was aware that certain “Jesus books” were called “Gospels” in his day (1 Apology 66.3; Dialogue with Trypho the Jew 10.2; 100.1), Justin preferred to designate them as απομνημονεύματα or “memoirs” of the apostles (1 Apol. 66.3; 67.3; Dial. 100.4; 101.3; 102.5; 103.6, 8; 104.1; 105.1, 5, 6; 106.1, 3, 4; 107.1). Why did Justin prefer this designation? The main debate has been whether Justin was influenced by the claim of Papias of Hierapolis that the Gospels were based on the memories of the apostles (i.e. Peter and Matthew), as well as what the evangelist Mark remembered from Peter’s preaching about Jesus (cf. Richard Heard, “The ΑΠΟΜΝΗΜΟΝΕΥΜΑΤΑ in Papias, Justin, and Irenaeus” NTS 1 : 122-129, Helmut Koester, Ancient Christian Gospels: Their History and Development [London: SCM, 1990]), or whether Justin understood the Gospels to be comparable to Greek philosophical memoirs such as Xenophon’s Memoirs of Socrates (Ἀπομνημονεύματα Σωκράτους) (cf. Niels Hydahl, “Hegesipps Hypomnemata” ST 14 : 70-113). For an extremely helpful overview of the terminology (i.e. ἀπομνημονεύματα, ὑπομνήματα, or commentarii) and function of a wide variety of commemorative writings and how Justin employed this terminology to advance his apologetic arguments (e.g., the Gospels as eyewitness records documenting the fulfillment of prophecy in history and evidence of the literacy of the apostles and their subsequent literate interpreters in the Christian assemblies), check out Wally V. Cirafesi and Gregory P. Fewster, “Justin’s and Ancient Greco-Roman Memoirs” Early Christianity 7.2 (2016): 186-212 (pre-publication version available on academia.edu).