The son of a feudal lord, Galgano became a knight, and is said to have led a riotous life. But once, according to legend, an invisible angel lifted him to his feet and led him to the hill of Monte Siepi. In a vision, he saw a round temple on the hill, with Jesus and Mary surrounded by the Apostles. The angel urged him to repent his sins, but Galgano protested that he could no more do this than to split a rock with a sword. To prove his point, he drew his blade and thrust at the stony ground, but the sword slid easily into the living rock, where it remains stuck fast to this day.

The sarcophagus with the sword said to have been driven into a stone by Galgano is inside of this chapel