Near the end of book II of his Gesta regum anglorum, finished around 1125, on pp 276-77 of volume 1 of this 2-volume set --
-- William of Malmesbury writes about a monk of Malmesbury named Eilmer who in 1066, upon seeing the comet we now call Helley's Comet, foretold a chaos of nations which would be the woe of many mothers. Halley's Comet is fainter every time it approaches the Earth, every 86 years. In 1066 it must really have been something to see. And a little later in 1066 the Battle of Hastings occurred, which was the beginning of the Norman Conquest, which did indeed brief grief to many English mothers. But ancient Greeks and Romans and Medieval Europeans always thought that comets heralded disaster, and there were usually enough disasters around that those who wanted to see cause and effect could pretty easily do so. If you had never read any ancient or medieval history before this, you might think Hmm, that's an interesting coincidence with the comet and the Conquest; if you've read a lot, you might think, as I do, Oh Jeez not again with the comets and the prophecies of doom, guys!
What's interesting about William's description of Eilmer is what comes next:
Is erat litteris, quantum ad id temporis, bene imbutus, aeuo maturus, immanem audaciam prima iuuentute conatus: nam pennas manibus et pedibus haud scio qua innexuerat arte, ut Daedali more uolaret, fabulam pro uero amplexus, collectaque e summo turris aura, spatio stadii et plus uolauit; sed uenti et turbinis uiolentia, simul et temerarii facti conscientia, tremulus cecidit, perpetuo post haec debilis, et crura effractus. Ipse ferebat causam ruinae quod caudam in posteriori parte oblitus fuerit.
(He was learned, by the standards of his time, of a good old age, and when quite young, mistaking fable for fact, had attempted, with remarkable audacity, to fly like Daedalus. By some means unknown to me he fastened wings to his hands and feet, waited at the top of a tower for the wind, and flew for more than a furlong. However, made unsteady by the wind and swirling air, and simultaneously by the consciousness of his own temerity, he trembled and plunged to the ground and broke both legs. He was lame for the rest of his life. He himself said that the flight had been ruined because he'd forgotten to put a tail behind the wings.)
If that really happened, and Eilmer really did fly for a furlong, 220 yards, when the highest tower in town was less than 1/10 that tall, then Eilmer was a true badass and far ahead of his time. 220 yards from a 60-foot tower is not all that bad for someone with some experience and skill using a 21st-century hang glider.
But did it really happen? William is known for his accuracy and scrupulous attention to detail. But writing perhaps a century or more after Eilmer's flight, he was relying on hearsay of hearsay. It's easy for me to imagine the length of the flight having been exaggerated by onlookers astonished by the fact that someone was attempting such a thing at all. I'd say the flight probably happened, but that details like the length of the flight in William's description have to be, as they say, approached with caution.
If it happened, you really have to hand it to Eilmer not just for ingenuity, but for commitment. Four and a half centuries later, Leonardo da Vinci made some very nice drawings of flying machines, but he never actually built one, strapped himself into it and jumped off of a dangerously high place. I know that there are all sorts of stories about Leonardo having done exactly that, but those stories aren't true.