What religious vision did ancient sources say Constantine I experienced before the Battle of Milvian Bridge?

Ancient sources provide varying accounts of the religious visions experienced by Constantine I prior to the Battle of the Milvian Bridge:

• Lactantius: In De mortibus persecutorum, the Christian apologist records that Constantine had a dream on the night before the battle. He was commanded to mark the Christian monogram—the Chi-Rho—on his soldiers' shields as a divine defense against his enemies.12
• Eusebius of Caesarea: In his later work, Vita Constantini, Eusebius describes a vision seen by Constantine and his army while on the march. They witnessed a cross-shaped trophy of light hovering above the sun, accompanied by the Greek inscription En toutō nika ("In this, conquer"). Eusebius also recounts a subsequent dream in which Christ appeared to the emperor, leading him to adopt the labarum as a battle standard.2

Additionally, a pagan orator in 310 referenced a vision of Apollo received by Constantine at a shrine in Gaul, suggesting that accounts of divine intervention were part of the broader religious competition of the era.1