The assertion that the works of mediæval architects have been destroyed or modernized to such an extent as to leave a wide gap between the classic and Renaissance periods, must have been made by persons unacquainted with Rome; the churches and the cloisters of S. Saba on the Aventine, of SS. Quattro Coronati on the Cælian, of S. Giovanni a Porta Latina, of SS. Vincenzo e Anastasio alle Tre Fontane, of S. Lorenzo fuori le Mura, are excellent specimens of mediæval architecture. Let students, archæologists, and architects provide themselves with a chronological table of our sacred buildings, and select the best specimens for every quarter of a century, beginning with the oratory of Aquila and Prisca, mentioned in the Epistles, and ending with the latest contemporary creations; they cannot find a better subject for their education in art and history. From the point of view of their origin and structure, the churches of Rome of the first six centuries may be divided into six classes:-- I. Rooms of private houses where the first prayer-meetings were held. II. Scholæ (memorial or banqueting halls in public cemeteries), transformed into places of worship. III. Oratories and churches built over the tombs of martyrs and confessors. IV. Houses of confessors and martyrs. V. Pagan monuments, especially temples, converted into churches. VI. Memorials of historical events. In treating this subject we must bear in mind that early Christian edifices in Rome were never named from a titular saint, but from their founder, or from the owner of the property on which they were established. The same rule applies to the suburban cemeteries, which were always named from the owner of the ground above them, not from the martyrs buried within. The statement is simple; but we are so accustomed to calling the Lateran basilica "S. Giovanni," or the oratory of Pudens "S. Pudentiana," that their original names (Basilica Salvatoris, and Ecclesia Pudentiana) have almost fallen into oblivion. I shall select from each of the six classes such specimens as I believe will convey an impression of its type to the mind of the reader.