Augustaion

thumb|right|250px|Map of the administrative heart of Constantinople. The Augustaion () or, in Latin, Augustaeum, was an important ceremonial square in ancient and medieval Constantinople (modern Istanbul, Turkey), roughly corresponding to the modern Aya Sofya Meydanı (Turkish, "Hagia Sophia Square"). Originating as a public market, in the 6th century it was transformed into a closed courtyard surrounded by porticoes, and provided the linking space between some of the most important edifices in the Byzantine capital. The square survived until the late Byzantine period, albeit in ruins, and traces were still visible in the early 16th century.

==History== The square dates back to ancient Byzantium, before its conversion into an imperial capital by Constantine the Great. When Roman Emperor Septimius Severus (r. 193–211) rebuilt the city, he erected a large square surrounded by porticoes, hence named the Tetrastoon ("four stoas"). In the center of the square stood a column with a statue of the god Helios. In the 320s, Constantine adorned his chosen new capital with many new monumental buildings. His activities included new structures around the Tetrastoon, while the Augustaion was likely carved out of its eastern part at that time, and named after a Porphyry column supporting a statue of his mother, the Augusta Helena. The Augustaion was rebuilt in 459 under Emperor Leo I (r. 457–474), and again in the 530s, after being destroyed in the Nika riot, by Emperor Justinian I (r. 527–565). In its original form, the square was open to the public and functioned as the city's food market (agora), but after Justinian's reconstruction, it became more of an enclosed courtyard where access was restricted. Byzantine writers from the 7th century on refer to it as explicitly as a court or forecourt () of the Hagia Sophia.