The Book of Aneirin is the one that has the Goddodin, a long poem about a war that took place around Catterick in the sixth century. It's a great poem, if somewhat enigmatic. We don't know what the war was about or why they were fighting, we just know the names of some of the people who went there and died, oh dear yes, they certainly did die.
Men went to Catraeth, they were battle ready.
Green mead was their drink, bitter was its aftertaste.
And after exaltation, there was silence.