Early Christian Monuments in Rome
Educated Rome travellers, especially with an interest in early Christianity, often face the problem that non of the sometimes very impressive remains are included in the TOP 10 ‘must see’ list of established travel guides. Or to be fair, not at all. This overview aims to provide a (partly commented) list of the most remarkable material remains of Late Antique Christianity in Rome. Evidently, this list is neither exhaustive, nor aims to be, but reflects rather a selection guided by my preferences and interests. Certainly, all monuments on this list are worth a detour for any connoisseurs intrested in Rome’s early Christian past. Some of them, such as the Sant’Agnese complex, is definitely worth a half-day excursion.

Notable churches
Sant’Agnese Complex (via Nomentana 349)
Santa Cecilia al Trastevere (Piazza di Santa Cecilia 22)
San Clemente (Via Labicana 95)
Santi Cosma e Damiano (Via Dei Fori Imperiali 1)
Santa Maria Antiqua is located between the Palatine and the Forum, and therefore now part of PArCo (Parco archeologico del Colosseo). The ‘Forum Pass SUPER ticket’ and the ‘Full experience’ ticket includes the entry to the church.
San Paolo fuori le mura (Piazzale di San Paolo 1)
Santa Prassede (Via di Santa Prassede 9/A)
Santa Pudenziana (Via Urbana 160)
Santa Sabina (Piazza Pietro d’Illiria 1)
Santo Stefano Rotondo (via di Santo Stefano Rotondo 7)
Catacombs
This website offers (theoretically) up to date information the catacombs open to the public in Rome (and beyond).

My personal favorite is Priscilla (Via Salaria 430), which is fairly off the beaten path. In contrast to other catacombs around via Appia, visits here usually take place in small groups. It is easy to combine a visit with the Sant’Agnese complex and spend an afternoon in an authentic Italian quarter far away from streams of tourists.
SS Pietro e Marcellio (Via Casilina, 641) is an excellent choice for connoisseurs, as this catacomb accomodates the highest number of lavishly decorated cubicula, many of which is also shown during the guided tour. The catacomb is truely off of any beaten path, but, in my opinion, it is absolutely worth a/the detour. Please note, a researvation is mandatory.

Musea/Excavations

Excavations of the Vatican necropole under the Basilica di San Pietro (= ‘Tomb of Peter‘). Please note, visit only upon reservation. In my experience, tickets should be ordered well in advance at the Ufficio Scavi.

The Via Triumphalis necropole was destroyed, or more precisely, buried by a landslide. Today, the site represents one of the best preserved non-Christian necropole in Rome open to the public. Although not Christian, it offers an interesting contrast program to the catacombs, as it shed light on the enormous economic inequality within Rome’s less priviledged population. Theoretically, tickets can be purchased on the website of the Vatican Museums, but when I last checked, there was no single date available in the online calendar.
Yet another ‘nerdish’ thing is the Crypta Balbi (Via delle Botteghe Oscure 31). This is one of the most intriguing museums of Rome dedicated to the history and development of the urbs. It does not focuses on Christianity, but inevitably, it also deals with the Christian(isation of the) city. Absolutely underrated. But most unfortunately closed until further notice due to refurbishment.