Hidden in a spot that could not be approached during my visit there is another emperor, the Emperor Alexander. I found a site with some more information, i.e. "Alexander, the third son of Basil I, was born in A.D. 870 or 871. He was crowned as co-Emperor, at about the age of nine, before November of 879 and probably before August of that year, thus sharing the throne with his father and his elder brother Leo VI. He remained co-Emperor during Leo's life despite the hostility that existed between the brothers, and after Leo's death he ruled as sole Emperor for a period of thirteen months, from II May 912 until his death on 6 June 913, at which time, therefore, he must have been about forty-two or forty-three years of age. The mosaic portrait shows Alexander as a man of mature years and must, therefore, be ascribed to the late years of his life. It seems most probable, however, that it represents him in his capacity as sole Emperor and should be dated in the brief period of his reign."