That side gained an edge during this event by singing a song that caused a magic cauldron of immortality to fail, so that only foul smoke was produced when dead men were thrown in it.
One source says that a participant in this event was serving as the champion of Beli, the supreme god of light. It might have been caused by the theft of a plover or lapwing, or the theft of a white roebuck and a greyhound dog, which one side refused to return. That side gained an edge during this event by singing a song that caused a magic cauldron of immortality to fail, so that only foul smoke was produced when dead men were thrown in it. That side finally triumphed by figuring out the name of a woman called (*) Achren, resulting in victory for the sons of Don. This event, described in the Book of Taliesin, sees the brothers Amaethon and Gwydion defeat the Lord of Annwn. FTP, name this event in Celtic myth in which the forest morphs into an army. 
One source says that a participant in this event was serving as the champion of Beli, the supreme god of light.
Battle of the Trees Â [or Cad Goddeu, or Cath Godeau, accept any descriptive answers indicating that trees or plants are battling, also accept answers such as "War Between Gwydion/Amaethon and Arawn or the forces of Annwn"]