When did Justinian I become caesar and co-emperor of the Byzantine Empire?

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Mosaic detail of Emperor Justinian I with a jeweled crown and halo, wearing ornate robes, from the Church of San Vitale in Ravenna, Italy. — Justinian I Justinian I, detail of a mosaic in the Church of San Vitale, Ravenna, Italy.

Justinian I was named caesar of the Byzantine Empire in 525 by his uncle, Emperor Justin I. He was subsequently elevated to the rank of co-emperor on April 4, 527. Following the death of Justin I on August 1, 527, Justinian I became the sole emperor.12