THE SCENE: According to this passage by the medieval historian Walter Bower, the Picts and the Scots lived together peacefully for 500 years… until a dispute about a dog drove them to war.
THE TEXT: While the nations of the Scots and Picts were living peacefully together in their two kingdoms, and protecting their regions on all sides with united strength, it happened by chance that on a pre-arranged day certain noblemen from both nations met together, as was their custom, on the borders of the two kingdoms for some hunting. While the dogs were unleashed and they were running about in all directions chasing wild beasts for about the length of a day, a certain hound, which used to follow the scent on the tracks of the beasts, was stolen away by the Picts, and was immediately discovered in their possession. When the Scots demanded it back, the Picts refused to return it. A dispute arose, and the Scots tried to snatch it from them by force. But the Picts for their part made no attempt to mitigate their wrong-doing by giving them satisfaction, but rather made matters worse by even greater savagery, and they lost no time in starting to fight. As a result many on both sides of those who had met together were slain by each other’s swords. For this was the occasion and beginning of the first dispute between them, as we read, after they had lived together in unbroken peace for five hundred years, and had joined harmoniously together in resisting all other nations with their united power.
– Scotichronicon, Walter Bower, 15th Century AD