Merlin was the first one the enemy knights met, and they asked him who was attacking them. And Merlin answered that they belonged to King Arthur, who was coming to claim the land of anyone who harbored anything against him.

When they heard what he said, they turned about, spurring their horses, and they came back to their army and began shouting, “We’ve been betrayed! Lord knights! get your armor on! You’ll need it now more than ever before, for the enemy is coming!”

They sprang from their beds and ran to get their arms first and not their clothes. Luckily, their horses were saddled, but, for all their rushing, they could not get themselves armed and ready before the enemy was at their throats. They were hampered all the more by a great wind and storm that Merlin sent against them, for all their tents fell in on their heads, and a fog came down on them so thick that they could not see one another without great effort, and it hindered them so much as they tried to arm themselves that they suffered great harm. For King Arthur’s men rushed headlong into their midst and brought down or killed as many as they got to.

Vulgate Merlin