She stands in the apse of a church in Ravenna, carrying a golden chalice, surrounded by her court. She wears a crown of pearls and jewels. Her face is long, pale, her eyes enormous and absolutely direct. Around the hem of her robe, embroidered in gold, are the three Magi — bringing gifts, just as she is.

Theodora was one of the most powerful women in the history of the Byzantine Empire. She had been an actress — a disreputable profession in late antiquity — before she became Justinian's empress and, by most accounts, his equal. She influenced law and theology and politics to a degree that shocked and outraged many of her contemporaries. And here she is, in the most sacred space of a church, making the offering. On the left wall, facing her across the apse, her husband Justinian does the same. They are equal in the image.

The mosaic is a political document, a theological statement, and a portrait. It is also one of the most dazzling surfaces human hands have ever produced: gold and silver and lapis and emerald and wine-red glass, shimmering in the Italian light as it has for nearly fifteen hundred years.

Glass and stone tesserae, gold-leaf glass, semi-precious stones set in lime mortar. The slightly convex curve of the apse wall required the mosaicists to carefully adjust the size and angle of each tile to maintain the illusion of flat alignment when viewed from the floor. The gold background tiles are set at a slight upward angle to catch light from the windows below. The entire program took approximately twenty years to complete.

Theodora's position carrying the chalice places her in the role of a deacon — a claim of sacred authority that was, for a woman, extraordinary. The Magi on her hem mirror her gesture of gift-giving, equating her offering with theirs. Her position on the south wall (associated with the feminine, with mercy) mirrors Justinian's on the north. Together they frame the altar, making the imperial couple the permanent, eternal attendants of the Eucharist.

Ravenna was the western capital of the Byzantine Empire under Justinian, who had reconquered northern Italy from the Ostrogoths. San Vitale was built as an assertion of Byzantine power and orthodox theology in a region that had spent decades under Arian Christian rule. These mosaics were propaganda of the highest order — but propaganda made by the greatest craftsmen the empire possessed, which is how propaganda becomes art.

The San Vitale mosaics were among the first major Byzantine works seen by Western European artists as the medieval period began — Charlemagne visited Ravenna and modeled his own palace chapel at Aachen directly on San Vitale. The image of the standing royal court, flat and frontal against gold, became the standard format for representing sacred and secular authority throughout the Carolingian and Romanesque periods.