The sword in the stone lies at the center of the King Arthur story, serving as both the instrument of fate that allowed him to assume the throne and his introduction to the supernatural world.
But King Arthur's sword in the stone is fiction inspired by a real life, and somewhat more boring, sword embedded in stone that was once wielded by a knight who saw the light too- St. Galgano Guidotti in the 12th century.
Guidotti was an arrogant and violent knight who did bad deeds until he started having holy visions:
The affluent nobleman is said to have had visions of the Archangel Michael, the warrior saint. One of these visions supposedly led him to the Twelve Apostles on the hill of what is now known as Rotonda di Montesiepi.
It is here that Michael suggested that Guidotti should give up his life of wealth and dedicate his existence to God instead. Guidotti snickered at the Archangel’s request and stated that the task would be as difficult as splitting a stone. To prove his point, the knight thrust his sword into a rock and, to his surprise, cut through it like butter.
Sometime after, while on horseback, he wandered to a hilltop much like the one he had seen in this dream. He was so struck that by the sight that he decided to plant a cross. However, without a cross or any wood handy, he unsheathed his sword plunged it into a stone, where it has remained ever since.
Guidotti's sword, and the stone it's still embedded within, resides in Montesiepi Chapel in Siena, Italy, which was built to house the relic after Pope Lucius III declared Guidotti a saint in 1185, just one year after his death.