The Catacomb of SS. Peter and Marcellinus, sometimes called “ad duas lauros,” from the original name of the district, is in the immediate neighbourhood of the famous Torre Pignatara, the tomb of S. Helena, this appellation being derived from the pignatte or earthen pots used in the building. The magnificent porphyry sarcophagus now in the Vatican was removed from this tomb. SS. Peter and Marcellinus, from whom this once celebrated catacomb is named, suffered in the persecution of Diocletian. S. Peter was in orders as an exorcist. S. Marcellinus was a priest. Pope Damasus, in his inscription originally placed on their crypt, tells us he learned the particulars of their martyrdom from the executioner employed by the State. This cemetery has lately been partially explored. The bodies of the two saints who gave their names to the catacomb were carried away, and are now in Seligenstadt, near Mayence. The saints termed “the Quatuor Coronati” were in the first instance buried here, but their remains were subsequently translated by Pope Leo IV to the church on the Cœlian. This cemetery is of considerable extent. The Itineraries enumerate the names of several martyrs once evidently well known. They also speak of many other martyrs buried here, using such expressions as “innumerabilis martyrum multitudo sepulta jacent”--“alii (Martyres) innumerabiles,” etc. THE VIA TIBURTINA The Via Tiburtina leads to Tivoli. It quits Rome by the Porta S. Lorenzo, which stands on the site of the ancient Porta Tiburtina. On this road are two large cemeteries, that of S. Cyriaca and that of S. Hippolytus. S. Cyriaca was a Christian widow. The importance, however, of this catacomb is mainly derived from its possessing the tomb of S. Laurence. S. Laurence suffered martyrdom A.D. 258, three days after the death of Pope Sixtus II, to whom he was attached as deacon. A very general tradition relates that Laurence suffered on a gridiron. An extraordinary popularity is attached to his memory. Marucchi, one of the latest scholars who has written on the catacombs, does not hesitate to say that the veneration paid to him was almost equal that accorded to the apostles. There is scarcely a city in Western Christendom which does not possess a church bearing his honoured name. In Rome itself there are six of these. Over the crypt containing the tomb of S. Laurence, Constantine the Great built a little oratory or memoria, which soon became too small for the crowds of pilgrims. A second church was erected by Pope Sixtus III, A.D. 432, by the side of Constantine’s Memoria which was ever known as “Basilica ad Corpus.” The second church was termed the “Basilica Major.” Three of the fifth century Popes of Rome were buried in the “Basilica ad Corpus.” In the thirteenth century the two churches were made into one by Honorius III, A.D. 1218.