This page from my Hagia Sophia website shows the sources that were used in the creation of the website.
Parade Entry Hall
The principal entrance to the Palace is found on the southern facade along the the Moskova. Sixteen steps lead up to the Parade Entry Hall.
The recessed vaults of the entry hall are born by four monolithic columns of grey granite from Serdobol, Viborg Government, with doric capitals. Their bases are Carerra marble. Opposite the columns, eight pilasters of the same granite, with marble capitals and bases. In the corners, four identical pilasters. The walls are of stucco, painted to imitate white marble. Next to each column is a solid bronze candelabra. Grey marble flagstones form the floor.