The word 'Confessio' refers to the Confession of faith by St. Peter which lead to his martyrdom. St. Peter's tomb is behind the Niche of the Pallium.

In this niche is a silver coffer with fabrics (each known as a "pallium") woven from the wool of lambs blessed on the feast of St. Agnes (Jan 21) and bestowed upon patriarchs and metropolitans as a reminder of the Church's unity.