Ex­te­rior view of the Hagia So­phia, built 532-537 AD under the di­rec­tion of Jus­ti­nian I, and con­side­red a mas­ter­piece of By­zan­tine ar­chi­tec­ture. It was the first large rectan­gu­lar buil­ding with cros­sing to be co­vered with a dome. The 107-ft. square cros­sing has four mas­sive stone piers sup­porting four semi-circular ar­ches and four pen­den­ti­ves upon which the dome rests. The apex of the dome is 180 ft above the floor. The large half dome seen on the side ofs the buil­ding acts as a but­tress.

In­side the Hagia So­phia loo­king up­ward into the dome. One of the world's great domes, built in 563, it has a dia­me­ter of 107 ft, a rise of 50 ft at the crown, and co­vers a 107-ft. square cros­sing. It is con­struc­ted of bricks 27 in square at the base and 24 in square at the apex, all 2 in thick, with ap­pro­xi­mately 2 in thick mortar joints. and the apex is 180 ft above the floor. The 40 ra­dial cur­ved ribs ter­mi­nate through the 40 win­dows at the base of the dome. This dome re­pla­ced the ori­gi­nal and flat­ter dome, with a rise of ap­pro­xi­mately 41 ft, which col­lap­sed in an ear­t­h­quake in 558.