When Sir Tristan felt himself struck in this way he was even angrier than he had been before, and rode up to Giglain who was
on the point of passing beyond him to complete his charge, and gave him such a mighty blow on his helmet that the part he had hit was knocked to the ground. The blow was powerful and struck with great anger and great strength, since Tristan was full of fury. But Giglain leapt back a little, with the result that Tristan’s sword slipped downwards and caught Giglain’s horse in the neck and cut right through it without difficulty, for Sir Tristan was a very strong knight. The horse fell to the ground, dead, and the knight flew down beside it, without however being unduly hurt, as the blow had not struck home.

Prose Tristan