So that everybody could see that it was his efforts alone which held back the Saxons, he had Bran's head exhumed.
I was reminded of that story, as I so often am, thinking about some of the Facebook carping about the Queen's 90th birthday last week. Because the monarchy has a secondary, somewhat mystical function, which is little discussed or understood: it keeps us safe from fascism and authoritarian mysticism.
I consider myself of the Left, but I can't say I find much pleasure in my fellow lefties' complaints. The monarchy provides us with colour, extravagance, fun and a sense of mystical importance. There will be puritans among us who prefer life without maypoles, theatres and monarchs, but I'm not one of them. I find the dour disapproval of the monarchy in principle very hard to understand.
I know there is the old Charter 88 idea that monarchs imbue us with the habit of deference. In fact, I have a feeling the opposite is true. I feel more equal with David Cameron as a fellow subject than I would if he was president. I feel more equal with the inhabitants of Buckingham Palace than I would if they were sponsored by McDonalds after an election campaign backed by Murdoch. We can be citizens as well as subjects.
There is certainly a problem about prime ministers borrowing the powers of the monarch. That is a separate issue altogether, and doing away with the monarchy won't solve it.
But let's get back to Bran the Blessed (as distinct from Brian Blessed, a very different personage). You can't help noticing that nearly all the former imperial powers of Europe which got rid of their monarchies became fascist states - Germany, Italy, Spain and many of those in central Europe too. The exception is France, and I'm not absolutely sure that is an exception, but is certainly complicated by having two rival royal and imperial versions.
Why is this? Because former empires are subject to some fiercely nostalgic, not to say atavistic, undercurrents. There are dangerous, sometimes militaristic, yearnings for former greatness which attract dangerous and unpleasant people.
But monarchies dissipate this energy safely. People wave flags instead. They owe allegiance to the living monarch, not to imagined past glories. Monarchies inoculate former empires against authoritarianism.
Of course, there are some on the puritanical Left who want to protect the nation from fascism by their own campaigning power alone. I'd prefer not to take the risk.