Roman ruins aside, this is Ravenna's oldest intact building, constructed over the site of a former Roman baths' complex in the late 4th century. Built in an octagonal shape, as was the custom with all Christian baptisteries of this period, it was originally attached to a church (since destroyed). The mosaics, which thematically depict Christ being baptised by St John the Baptist in the River Jordan, were added at the end of the 5th century.
