These are the 3 kings, or magi. Their clothing is conspicuously Sasanian as are the gifts they bear. It is interesting that each one wears the Phyrgian cap, a symbol of being from the east and/or of being free-born.
What I find fascinating are the date trees. These are not found Ravenna, yet appear to symbolize fecundity and wealth. It's interesting that a Germanic patron would include this flora in his tribute image. What this probably represents is artistic freedom. Theodoric probably told the artisans to include what they believed was appropriate and correct. Whether he ever saw a date tree is rather doubtful.
Here's the front of the church. The tower was added in the 10th century, after casting technology advanced far enough to for the production of bells. Nothing is so sacred that the latest technology can't be incorporated.