Read this: Very few early Byzantine mosaics survived the Iconoclastic destruction of the 8th century. Among the rare examples are the 6th-century Christ in majesty (or Ezekiel's Vision) mosaic in the apse of the Church of Hosios David in Thessaloniki that was hidden behind mortar during those dangerous times. Nine mosaic panels in the Hagios Demetrios Church, which were made between 634 and 730, also escaped destruction. Unusually almost all represent Saint Demetrius of Thessaloniki, often with suppliants before him.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): Why was Christ in majesty protected from the iconoclastic destruction?
hidden behind mortar