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.
Byzantine emperors ascending the throne were crowned at the Opus Alexandrinum.
Concentrated natural seawater is the same as seawater from the ocean.