We’ve just added a new 3 hour tour that has a theme of ‘Christian Rome’. This guided tour visits Santa Maria Maggiore and San Giovanni in Laterano (the ‘cathedral of Rome and of the world’), the ‘Holy Stairs’, the Appian Way, before going on to a guided tour ‘underneath’ Rome, the famous burial catacombs of San Callisto.
Link: tour of Christian Rome and the Roman catacombs.
Below is a video from the ubiquitous Rick Steves – the first half sees him looking around some of the Roman catacombs.