of the courts of the Palatine with such intarsio work, but his cousin Alexander Severus, following his example, adorned with it all the terraces and walks around, and the pavements within, the isolated villas called Diaetae, dedicated to his mother Mammaea, which he added to the Palatine buildings.  We have examples of this beautiful kind of tesselated pavement in some of the chambers of the Baths of Caracalla; and it is highly probable that the Opus Alexandrinum in the transept and middle nave of the Church of Santa Maria in Trastevere is in part at least contemporaneous with Alexander Severus, who conceded the ground on which the original oratory stood to Pope Calixtus I. in 222, for the special use of the Christians.  If this be so, we have in this first place of Christian worship established in Rome the first instance of the application of Opus Alexandrinum to the decoration of a church.  In the middle ages the fashion was beautifully imitated by artists of the Cosmati family and their school; and the mosaic pavements of this kind in the medieval churches of Rome are no older than this period.  But we have reason to believe that the Opus Alexandrinum in two of the chapels of Santa Maria degli Angeli was taken from the Baths of Diocletian; while the splendid pavement of the whole church, naves, transept, and choir of Santa Croce in Jerusalemme, formed originally part of the decorations of the Sessorian Palace of Sextus Varius, the father of Heliogabalus, after whom the church is sometimes called the Sessorian Basilica.  The flooring of the whole upper church of San Clemente was transferred from the older subterranean church, which derived its pavement from some of the ruins of the Palatine or the Forum; and the serpentine fragments, which enter very largely into the composition of the curious old mosaic floor of Ara Coeli must have had a similar origin as far back as the time of its founder, Gregory the Great.  The Lapis Lacedaemonius must have been very abundant in Rome during the time of Alexander Severus—­judging from the quantities that are made up into mosaics in the churches, and the heaps of broken fragments that are found on the Palatine and at the Marmorata.  The circular space around the obelisk in the Piazza of St. Peter’s to a considerable extent is paved with it; and specimens of it frequently occur among the ordinary road-metal in the city and neighbourhood.

Sicilian jaspers, so called, though really marbles, and purely calcareous, because of their resemblance in colour and form of the blotches to jasper, were wrought in great variety in the quarries in the neighbourhood of the celebrated Taormina, and were transported in the form of columns to Rome.  Siliceous jaspers, obtained from the crystalline rocks of Asia Minor, Egypt, and Northern Italy, were also used for columns; and their brilliant red, green, and yellow hues, highly polished, contrasted beautifully with the white marbles of the interiors of the palaces.  An even more