Eusebius' account of constantine's vision and dream before the battle at Rome in his Life of Constantine has become powerfully influential among modern historians. This is an odd outcome. Eusebius was still revising Life when he died probably in May 339, more than twenty-five years after the battle. He was the bishop at Caesarea in Palestine and hence knew little about events at distant Rome. He clearly used his biography of the emperor to promote a theological and political agenda about the nature of Christian emperorship. Late, far away, sectarian, partisan: Eusebius' account should have struggled to become so significant.

The redeeming factor of his account of the vision and the dream was the declaration that he had heard it directly from Constantine himself. Eusebius claimed to be recording the memories of an eyewitness. But this assertion in turn raises another set of issues about the dating of Constantine's recollections, the reliability of Eusebius' reporting, and the accuracy of his interpretations. Constantine recalled his memories for Eusebius and other bishops for specific reasons at a specific moment long after the battle; Eusebius subsequently recorded the emperor's stories for different reasons at a different moment after the emperor's death. The account of the emperor's vision and dream in Life hence represented three distinct layers of particular circumstances: Eusebius' remembrance of Constantine's memories of events from long ago.