What is probably the most-overlooked of the National Roman Museums, the Crypta Balbi is a fascinating and worthwhile stop.
The museum sits above the Theater of Balbus (13 BC), which you can still visit.
The museum features a lay-out of Rome, showing you what it looked like in ancient times, in the Middle Ages, and how it has evolved today. The artifacts are extensive, including the Forma Urbis Romae, a 60×45 ft map made of marble that was mounted in the Forum in the 3rd century for visitors to the city.
Web Site: http://www.coopculture.it/en/heritage.cfm?id=50
Location: Via delle Botteghe Oscure, 31 Rome
Opening times (subject to change): Tues – Sun 9 am – 7:45 pm Closed Mon.
The Catacombs Of St.Callixtus
The catacombs of St.Callixtus are among the greatest and most important of Rome. They originated about the middle of the second century and are part of a cemeterial complex. In it were buried tens of martyrs, 16 popes and very many Christians.
They are named after the deacon Callixtus who, at the beginning of the third century, was appointed by pope Zephyrinus as the administrator of the cemetery and so the catacombs ofSt.Callixtus became the official cemetery of the Church of Rome.
In the open area are two small basilicas with three apses, known as the “Trichorae”. In the Eastern one were perhaps laid to rest pope Zephyrinus and the young martyr of the Eucharist, St.Tarcisius.
The underground cemetery includes several areas. The Crypts of Lucina and the area of the Popes and of St.Cecilia are the most ancient areas.
Web Site: http://www.catacombe.roma.it/en/index.php