Sts Lawrence and Stephen were venerated throughout Rome and the popes accorded them particular honour. Their martyrdoms were frescoed in the private papal chapel known as the Sancta Sanctorum (Holy of Holies) in the Lateran Palace, the official residence of the popes through the end of the Great Schism. The chapel was commissioned by Pope Nicholas III (reigned 1276-80). It preserved the miraculous, painted portrait of Christ, believed to have been completed by angels, and some of the most treasured relics from the Holy Land, including a coal from the fire that roasted Lawrence and drops of Stephen's blood.
The architect of the chapel, which was consecrated in 1279, was Cosma di Pietro Mellini. The interior is strongly influenced by Gothic architecture. The main room, which measures seven by seven metres terminates on its east side in an oblong rectangular altar room that is marked off by two porphyry columns. The walls of the chapel are clad with antique marble. Over the main room is a genuine Gothic quadripartite ribbed vault, in contrast to the altar room, which has a barrel vault with mosaics on a gold ground. The floor decoration is entirely in the Roman artistic tradition.
The frescoes, executed in 1278-79 by anonymous masters, thus represent just part of the chapel decoration. Complemented by the lavish marble and mosaic decoration, they are restricted entirely to the upper zone. On the east wall we see the donor being presented by Peter and Paul opposite a Christ enthroned. The south wall shows the Crucifixion of St Peter opposite the Beheading of St Paul. On the west wall is the stoning of St Stephen and the Martyrdom of St Lawrence. The north wall shows the Martyrdom of St Agnes and St Nicholas Providing the Dowry.
The pictorial program is thus related on the one hand to the dedication of the chapel (the martyrdom of St Lawrence) and relics kept in the chapel (of the martyrdom of Sts Peter, Paul, and Agnes), and, on the other, to the Roman papacy and Nicholas III himself as the donor.
The most striking characteristics of the paintings are the borrowings from antiquity in the decorative system and the ornamental repertoire (fans, display vases, acanthus tendrils, dolphins, and doves). Differences in the execution of the frescoes reveal the participation of several painters.