Medieval frescoes in the Sancta Sanctorum chapel of the Lateran Palace, Rome.

The Sancta Sanctorum chapel (Italian: Chiesa di San Lorenzo in Palatio ad Sancta Sanctorum) is a side chapel from the Scala Sancta (holy staircase) of the Lateran Palace, Rome. The artwork of the Sancta Sanctorum in Rome was the basis for the art at Assisi. The spelling is sancta, the neuter plural form of the Latin adjective "holy": this is a reference to the multiple relics preserved there ("the most holy things") and to the Holy of Holies in Jerusalem, traditionally called in Latin both Sanctum sanctorum (the singular form) or Sancta sanctorum, named for the many precious relics preserved there.
According to medieval historians, this was “the most venerated sanctuary in Rome” and was, until the Renaissance, the private oratory of the Popes. Today it remains a testament to the splendour of the ancient Patriarchium and to a thousand years of papal history. The founder of the chapel remains unknown; however it was originally dedicated to St. Lawrence, and in the IX century it was called the Sancta Sanctorum, due to the numerous important relics housed within. The first mention of the chapel is found in the Liber Pontificalis, written in the time of Pope Stephen III (†772). More testimonies began to appear from the year 1000 onwards, particularly as regards the Holy week liturgy and the possession of the Lateran. Gregory IV (†844) had a private apartment built near the chapel to allow him to pray there and preside over the clerics of the Curia more easily.

The decoration of the Scala Santa was one of the major refurbishment exercises of the papacy of Sixtus V, led by Cesare Nebbia and Giovanni Guerra and occupying a crew of artists to decorate frescoes. Numerous preliminary drawings by Nebbia exist for these frescoes, though it is not exactly known with certainty who painted which fresco.

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