Gregory of Tours - 584, France, exact location unknown: A battle of lights
Type of Spiritual Experience
A description of the experience
from Wonders In The Sky - Unexplained Aerial Objects From Antiquity To Modern Times - and Their Impact on Human Culture, History, and Beliefs - Jacques Vallee and Chris Aubeck
Many witnesses. Brilliant rays of light hitting one another in the sky.
Given the lack of details, some natural phenomena (such as an aurora borealis) could produce this effect. However we cannot completely reject the case on the basis of the information given, and the source is impeccable.
Source: Gregory of Tours, History of the Franks, op. cit.