Among the Crown Jewels of the United Kingdom is a broken sword. Its blade is missing about six inches at the business end. There are several legends, but no known facts, about where this came from and how it came to be this way. Today, it's known as the "Sword of Mercy," and used in coronations because it is symbolic of a monarch's need to be merciful.
One legend holds that the sword in question belonged to Edward the Confessor. That's fairly likely; the sword itself is of approximately the correct vintage. Perhaps Edward broke the blade himself or had it forged that way precisely for the current symbolic resonance. It's also been said that the blade was broken off by an angel to show that a sovereign needs to show mercy.
But there's another legend about a similarly broken sword, and sometimes the two are said to be one and the same. We are told that Ogier the Dane, a knight of Charlemagne in the Matter of France, carried a sword which had been cut a bit short to fit his small stature; for this, the sword was named Curtana (or, in modern French, Courtain). The descriptions of Curtana are often consistent with the present-day Sword of Mercy.
There are two stories about the origin of Ogier the Dane's blade. One holds that it was forged along with Charlemagne's "Joyeuse" and Roland's "Durendal," possibly by the hand of Wayland the Smith, and that after Ogier swore fealty to Charlemagne, thereby putting aside a feud between their two families, Charlemagne gave the sword to Ogier (who shortened it) as a sign of trust.
The other holds that the sword had once been born by Sir Tristan, and that Ogier was already wielding it, shortened for his own use, when he very nearly slew the Frankish king as just vengeance for killing his brother. Ogier was stopped short by a voice calling from heaven for him to show mercy, and he became one of Charlemagne's followers thenceforth. Again, this story presents the sword as symbolic of the quality of mercy, but gives an entirely separate explanation for the missing tip.
These stories, alas, are missing one crucial feature: the sword now known to us as the Sword of Mercy is not of a style consistent with early Carolingian weapons, and does appear to be of late Anglo-Saxon make. But the thought of one blade passing through the hands of a Knight of the Round Table, of a Paladin of the Twelve Peers, and finally of every English monarch for a thousand years, is too good a story to let go.