The octagonal 5th-century baptistery replaced that of the 4th, which had been built into the baths of the House of Fausta, Constantine’s second wife. (Later, in another palace, she was strangled in the hot room of the bath, a conventional Roman device for suggesting accidental suffocation of an awkward relative.) Its chapels are decorated with mosaics of the period. The cloisters contain some of the finest examples of early 13th-century carved and inlaid decoration called Cosmatesque after the Cosmati, one of several families of traditional craftsmen.

(The cloisters of S. Cosimato, S. Paolo Fuori le Mura, and SS. Quattro Coronati are notable examples of this work, which often was accomplished with porphyries and marbles robbed from classical buildings.) On the exterior a 1732 facade is topped with 15 giant statues that were visible across the city. The piazza around which the Lateran buildings are grouped is decorated with another obelisk, the oldest and tallest in Rome (15th century bc), one of those erected by Sixtus V late in the 16th century. At the same time, he demolished the old patriarchate, from which the Sancta Sanctorum (the papal chapel) and the Scala Santa (Holy Stairs) were preserved. The Scala had been the principal ceremonial stairway of the palace, but about the 8th or 9th century it began to be identified popularly as having been brought from Jerusalem by St. Helena, Constantine’s mother, reportedly from Pilate’s palace and thus the stair climbed by the Saviour. The steps are protected by a wooden cover, and believers mount on their knees. The Scala Santa is not mentioned, however, in ecclesiastic, imperial, or personal writings from the 4th, 5th, or 6th century. Britannica enciclopedia