Pass through the marble gate and walk towards the empress’s position. Then keep walking and at the end turn right. You cannot go downstairs through the same ramp, so you keep walking having the museum shop on your left. When you arrive at the point that you see the balcony where the mosaic of Deesis stands, walk towards the green columns on your right. Stand facing the center of the museum in front of the green columns. Here turn right and look up. It is not easy to see this because it is not lightened and stays in the dark. You will see the mosaic of Emperor Alexander. You can listen to the story of the 20th point of interest.