The Baptism of Jesus
A few years later, the Gothic ruler of Ravenna, who was an Arian (Arians believed that Jesus was created by the Father and thus inferior to him, a view that was condemned as heresy at the Council of Nicea in 325) built his own baptistery. A very similar mosaic is in that building.
As you can see, the portrayals of the event are very similar. Jesus stands in the water and John and the Holy Spirit (in the form of a dove), along with an old man (who represents either a personification of the River Jordan or a pagan water god, who we see witnesses the true God in Jesus) are nearby.
There are some differences, though. In the Orthodox depiction, Jesus is older, with a beard, and John uses a paten to baptize Jesus (that paten is a 19th century addition by a overenthusiastic mosaic restoration artisan). The Arian baptistry depicts a young (beardless) Jesus and the Holy Spirit's shedding of light and grace upon Jesus' head is unmediated by the paten.
So in many ways, the Arian mosaic seems more appropriate to me. Don't tell anyone.