On the south arm of St. Mary’s transept, we can see Romanesque paintings that depict the martyrdom of St. Thomas Becket, assassinated by men of King Henry II of England in 1170.
In the central register we find three scenes of his death and martyrdom. On the left, the accusation by the king's men; in the centre, the murder and, in the right register, the deposition of the body in the tomb and the ascension of the saint’s soul.