This investigation of the pre-Patrician material in Irish annals first reviews the historiography, then examines the chronology of Roman imperial successions, and reveals a conflation of Eutropius’s Breviarium with Jerome’s Chronicle. Collation with Bede’s Chronicon maior shows these annals and Bede have a common source. The annals preserve more of this source and its chronological apparatus. The Alexandrian episcopal succession in AT derives directly from Rufinus’s History, and the errors suggest that he himself constructed it. The Hebrew succession in Bede and AI reveals divergences from Jerome’s chronology, not plausibly the work of Bede but appropriate to Rufinus. Hence the hypothesis that Rufinus compiled a chronicle in the early fifth century, that it came to Ireland with the 84-year paschal table of Sulpicius Severus, and that it was used in Iona in the mid-sixth century as the basis for the Iona Chronicle.