At the east end of the galleries, two small columns and a circle of green marble mark the spot where the empress sat during services; on the floor of the nave below, a circle of coloured stone to the right of centre is the Opus Alexandrinum, the place where the Byzantine emperors were crowned.
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Byzantine emperors ascending the throne were crowned at the Opus Alexandrinum.
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The Opus Alexandrinum marks the spot where the bishop would stand during church services.