This mosaic is overlooked by almost all visitors. It is situated on the first floor, on the east side of the northwest pier. It is hard to spot there, as there is no illumination and the light generally is dim.
Alexander succeeded his elder brother Leo VI in May 912. In June the following year Alexander died of apoplexy during a drunken game of polo. Strolling through Istanbul (that I use for this information) calls him a “mad and drunken despot”, concluding the mosaic must be from the period of tis reign because honouring him before of after that is inconceivable. He stands full length, flanked by four medallions bearing the legend “Lord help thy servant, the orthodox and faithful Emperor Alexander.”