The third bay of the right hand aisle is the vestibule of a large external chapel, built to house the relics of St Paul of the Cross, who was canonization in 1867. The Passionists brethren built an enormous new domed shrine-chapel for him in 1857. The architect chosen was Filippo Martinucci. It was completed by his son, Vincenzo Martinucci, in 1880 with decorative elements continuing for another two years.