December 18 is the feast day of Saint Gatian, the first Bishop of Tours. Saint Gatian reached Gaul in the mid-third century. He proceeded to convert many of the Gauls to Christianity.
Scott includes the Church of St. Gatian - the Cathedral of Tours - in his Quentin Durward. This cathedral was erected between the 13th and 16th centuries.
"...The towers of the church of Saint Gatien were also visible, and the gloomy strength of the Castle, which was said to have been, in ancient times, the residence of the Emperor Valentinian..."