A vision experienced at the Pantheon sent him to Aosta. He converted many pagans there and Charlemagne aided him in his mission. By divine command, he was then sent to the Holy Land to find the head of Saint John the Baptist. For this reason, Gratus is sometimes depicted with John the Baptist's head in iconography. He was accompanied by ( or ). Gratus found the relic concealed in the palace of Herod. Smuggling it out of Jerusalem, Gratus returned to Rome, where churchbells played of their own accord in celebration. Gratus presented John's head to the Pope; in doing so, the jawbone remained in Gratus' hand. This was interpreted as a sign, and the Pope allowed him to carry that precious relic back to Aosta. Gratus continued to govern the diocese, while periodically withdrawing to a hermitage with Jucundus.