Nicholas I Mystikos — modern representation - cropped & smugged
Photo Credit: By Nikolai Pavlovic (1835-1894) - "Bulgarien vom Beginn seines staatlichen Bestandes bis auf unsere Tage", 1917, Public Domain, https://commons.wikimedia.org/w/index.php?curid=14641832

Alexander of Constantinople — By Unknown author - Cropped from mosaic at Hagia Sophia
Photo Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=25504327

Stephen I of Constantinople —
Photo Credit: By 13th-century author - History of John Skylitzes - Public Domain, https://commons.wikimedia.org/w/index.php?curid=57991651

Hagia Irene — The cathedral church of the Patriarchate before Hagia Sophia was completed
Photo Credit: By Sébah & Joaillier - Library of Congress, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6327634

Coat of arms of the Ecumenical Patriarch of Constantinople —
Photo Credit: By Zografos 07 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=37973264

Hagia Sopia in 1852 — Square in Istanbul, with the Hagia Sophia mosque at right, part of an ornate pavilion at left, and several figures, some on horseback; print pasted onto backing sheet;Tinted lithograph with hand-coloring
Photo Credit: Print by Louis Haghe After: Gaspard Fossat - Public Domain, https://commons.wikimedia.org/w/index.php?curid=90296597

Construction of the Hagia Sophia — Depicted in codex Manasses Chronicle (14th century)
Photo Credit: By Original: Constantine Manasses - Scanned from book "Miniatures from the Manasses Chronicle", Ivan Duichev, "Bulgarski hudojnik" Publishing house, Sofia, 1962, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3511368

Hagia Sophia — View from Sultanahmet Square
Photo Credit: By Dennis Jarvis from Halifax, Canada - Turkey-3019 - Hagia Sophia, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=23450307

Pendentive Dome — A pendentive is a constructional device permitting the placing of a circular dome over a square room or of an elliptical dome over a rectangular room.
Photo Credit: By hu:User:Totya - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1604919

Geometry of Hagia Sophia — The geometric conception is based on mathematical formulas of Heron of Alexandria. It avoids use of irrational numbers for the construction
Photo Credit: By P.Cikovac - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=75031142

Coronation of Basil I as co-emperor — from the Madrid Skylitzes manuscript
Photo Credit: By Unknown, 13th-century author - History of John Skylitzes (Skyllitzes Matritensis (Biblioteca Nacional de España), Public Domain, https://commons.wikimedia.org/w/index.php?curid=27610612