The mosaics of San Vitale first confronted me on a Tuesday in late October, when the tourist crowds had thinned and the custodian was sweeping leaves from the narthex. The church was cold, the air heavy with wet stone and candle wax. Then I turned the corner into the apse, and the gold struck — not as decoration but as a kind of weather. The entire curved wall shimmered with tesserae set at deliberately irregular angles, each tiny cube catching the low autumn light from a different direction.
The Theology of Tesserae
The Byzantine mosaicist did not work the way a painter works. There was no canvas, no easel, no stepping back to judge the whole. Instead, the artist pressed cubes of colored glass — tesserae, from the Latin tessella — into wet plaster, one by one, working at arm's length from the wall. Gold tesserae were set at slight angles, tilted outward like tiny mirrors, catching candlelight and throwing it back into the nave. The craftsmen of Ravenna understood something about light that electric illumination has made us forget: a surface can be more luminous than its source.