It is a surprise how small Galla Placidia's mausoleum is. A cross-shaped brick chamber no bigger than a modest chapel, it stands hidden behind the church of San Vitale in a quiet corner, with plain walls that give no hint of what is inside. Step in and the dark opens into a deep blue night. The vault is covered in tiny gold stars on a field of lapis-coloured glass, and a gold cross shines in the dome above, with figures of the apostles and doves drinking from a fountain in the lunettes. The only light comes through thin alabaster windows, which turn the daylight amber.
It was built around the middle of the fifth century and named after Galla Placidia, the half-sister of Emperor Honorius and a formidable figure, who ruled in the name of her young son after a life that included capture by the Goths, marriage to one of their kings and a return to the imperial court. Tradition names the building as her tomb, though she most likely died in Rome and was buried there, and the three sarcophagi in the chamber probably held other members of the imperial family. The legend is better than the evidence, but the building does not need it.
The best mosaic is the Good Shepherd above the entrance, a Christ in gold and purple who sits among sheep in a green landscape and holds a cross like a staff, an image that is almost pastoral. It is a rare survival of the very early style, when Roman artists made Christian subjects with a classical sense of space.
The ride list takes you from here to the Vena del Gesso and Monte Penzola, and the contrast is fun. After the closed jewel of the mausoleum, you can ride into the open karst country, the bright cliffs and the hollows of gypsum, about an hour's ride out from the flat Romagna coast. The route climbs through chestnut and oak woods before the cliffs appear.
Practical points: queues can build in busy periods and are shortest early, and Ravenna's centre is closed to most traffic, so park outside and walk. The city of eighty thousand has fuel on all approaches.