Final answer:
The octagonal shape of the Orthodox baptistry at Ravenna symbolizes regeneration and resurrection within early Christian and Byzantine architecture, often featuring intricate mosaics with religious iconography.
Step-by-step explanation:
The significance of the octagonal shape of the Orthodox baptistry at Ravenna is deeply rooted in early Christian symbolism. The eight sides of structures such as the Palatine Chapel at Aachen, and indeed the baptistery in Ravenna, are thought to represent regeneration and resurrection, symbolizing the new life that comes with Christian baptism and referencing Christ's resurrection 'eight days' after Palm Sunday (when including Easter Sunday in the count).
This tradition of octagonal design is seen in early Christian mausoleums and baptisteries and is carried forward in Byzantine and later architecture. The octagonal shape and the dome of San Vitale in Ravenna, for instance, influenced subsequent religious architecture across Europe, as exemplified by the Palatine Chapel, with both structures featuring not only the octagonal plan but also intricate mosaics depicting Christian iconography and narratives, such as the baptism of Jesus or the Lamb of God surrounded by the tetramorph and the twenty-four elders mentioned in Revelation.