AD 312

Labarum

Constantine's reported dream prompts a Christian sign on his soldiers' shields

The two famous halves of the legend come from different books, written more than twenty years apart.

Lactantius: a dream, and a mark on shields

The earliest surviving account says Constantine was instructed in a dream, immediately before the Battle of the Milvian Bridge on 28 October 312, to mark a heavenly sign of God on his soldiers' shields.

Lactantius says he complied, using an X-like symbol whose upper part was bent or turned. The crucial Latin wording is corrupt at exactly that point; scholars variously reconstruct a Chi-Rho or a staurogram-like emblem. There is no cross in the sky here and no Latin motto.

Eusebius: a cross above the sun, and a standard

Writing in the late 330s, Eusebius tells it differently: Constantine saw a luminous cross above the sun with the Greek command usually translated "By this conquer," and then dreamed that Christ ordered him to reproduce the sign as a protective military standard.

He describes the resulting labarum as a cross-shaped standard topped by a jewelled wreath containing the intersecting Greek letters Chi and Rho. He does not say the Greek words were adopted as an imperial motto or painted on shields.

The motto is a translation, not a record

"In hoc signo vinces" is a traditional Latin rendering of Eusebius's Greek phrase. No ancient source says Constantine formally adopted it as a motto in 312.

No contemporary administrative record or surviving shield verifies the episode at all. The detailed panegyric of 313, delivered in Constantine's own presence, says nothing about a dream, a vision or marked shields.

Sources

Researched 23 Aug 2026 6 sources not yet audited Date disputed

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~0312-10-27.

What the sources leave uncertain

No contemporary administrative record or surviving shield verifies the episode.
The approximate date of 27 October follows Lactantius’s placement of the dream immediately before the battle of 28 October. Eusebius provides no precise date or location.
Lactantius’s crucial description of the emblem survives in a corrupt Latin passage. A Chi-Rho is probable to some scholars, but a staurogram or other cross-like form is also possible.
Lactantius reports a dream and shield markings; Eusebius reports a daytime sky vision, a subsequent dream and the making of a labarum. Combining all these details produces the familiar legend but not either ancient account.