Since it was forbidden to bury the dead within the city walls during Roman times, various cemeteries were set up along the arterial roads. We also find many of them along the Appian Way.
Most important are the Catacombs of Callixtus, most notable for containing the Crypt of the Popes, and the Catacombs of Saint Sebastian.
Picture: The Catacombs of Saint Sebastian
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Best of Via Appia Antica with Audio Guide
There is a free audio guide from SmartGuide, with which you can explore the Appian way for about 25 km, if you want. Here is the link.
Because of the great distances a bike trip offers many advantages. You can book bikes here* for example (Tripadvisor*)