Helen (248- 329 AD) was the mother of Constantine I ( Emperor in 306). He gave her the title of Augusta, ( i.e. Empress). In the year 324, when his son moved the capital of the Empire to Constantinople, she was given the opportunity to live in the Palatium Sessorianum, which then became her exclusive residence. In 327- 328 A.D. Helen undertook a pilgrimage to the Holy Land to visit the places of the Passion of Christ; during this trip, as the historian Eusebius says, she became involved in numerous acts of Christian piety and construction of churches and she rescued the relics of the Cross of Jesus.
History and legend mingle in the story of this miraculous discovery: from the Legenda Aurea by Jacopo da Varagine (XIII century), we learn how Helen rescued more than a cross on Golgotha and to recognize the one belonged to Jesus she put in contact with the wood a deceased man who, touching the True Cross, was resurrected.
Once in Rome the Empress adapted part of the Palatium Sessorianum as a chapel to host the relics(it was the first nucleus of the actual chapel of Saint Helen) and later was added a baptistery to this small room. The chapel has been modified several times over the centuries, In the XVI century the vault was decorated with a beautiful golden mosaic, made from a sketch by Baldassarre Peruzzi and showing at the center a very rare example of Smiling Christ in the act of blessing.