The name tells the story: Saint Paul outside the walls. According to tradition, Paul was beheaded on the road to Ostia, and a Christian woman buried him in her family's cemetery beside the Via Ostiense, about two kilometres from the old city wall. Constantine built a small church over the grave in the early fourth century, and by the end of that century three emperors had replaced it with a vast basilica, the largest in Rome until the new Saint Peter's. In 1823 a fire destroyed most of the building, and it was rebuilt in the nineteenth century as a faithful copy of the old one, with a forest of eighty granite columns along the nave.
What you notice first is the light. The nave is long and bright, with alabaster windows, a gilded ceiling and a floor of polished marble, and high on the walls runs a frieze of medallion portraits of every pope, from Peter to the present, a row of faces that has been extended over the years. Under the high altar lies the tomb of the apostle, and a stone slab, marked with the name Paulo Apostolo Mart, can be seen through a window. Look for the Byzantine-style mosaic on the triumphal arch, which survived the fire, and for the Gothic cloister next door, a delight of twisted columns and inlaid stone, tucked beside the abbey.
Because it belongs to the Holy See, the basilica has extraterritorial status, like the Vatican, though you will not notice it. Riding to it is a matter of dealing with Rome. The Via Ostiense is a wide, busy road, with trams and buses, and the traffic is the usual mixture of impatience and improvisation. Watch for the cobbles, called sampietrini, which are slippery in rain, and for the limited traffic zones in the centre that fine unauthorised vehicles. The Garbatella district nearby has a quiet, garden-city charm with its low houses and courtyards.
Fuel is no problem in a city of nearly two and a half million, and the area has cafes, pizzerias and trattorias that cater to locals rather than tourists. Testaccio, a short way off, is the place for an authentic plate of cacio e pepe or oxtail stew. Entry to the basilica is free, though the cloister and museum charge a fee, and dress rules require covered shoulders and knees. Come in the morning or late afternoon, and make sure you look up.