The Nea Ekklesia is inaugurated in Constantinople, setting the model for all later cross-in-square Orthodox churches.

The Nea Ekklēsia was a church built by Byzantine Emperor Basil I the Macedonian in Constantinople between 876 and 880. It was the first monumental church built in the Byzantine capital after the Hagia Sophia in the 6th century, and marks the beginning of the middle period of Byzantine architecture. It continued in use until the Palaiologan period. Used as a gunpowder magazine by the Ottomans, the building was destroyed in 1490 after being struck by lightning. No traces of it survive, and information about it derives from historical accounts and depictions.

Constantinople was a historical city located on the Bosporus that served as the capital of the Roman, Byzantine, Latin and Ottoman empires between its consecration in 330 and 1930, when it was renamed Istanbul. Initially as New Rome, Constantinople was founded in 324 during the reign of Constantine the Great on the site of the existing settlement of Byzantium and in 330 became the capital of the Roman Empire. Following the collapse of the Western Roman Empire in the late 5th century, Constantinople remained the capital of the Eastern Roman Empire, the Latin Empire (1204–1261) and the Ottoman Empire (1453–1922). Following the Turkish War of Independence, the Turkish capital moved to Ankara. Although the city had been known as Istanbul since 1453, it was officially renamed Istanbul on 28 March 1930. The city is today the largest city in Europe, straddling the Bosporus strait and lying in both Europe and Asia, and the financial center of Turkey.

A cross-in-square, crossed-dome, tetrastyle, or quincunx floor plan was the dominant form of church architecture in the middle and late Byzantine Empire. It featured a square centre with an internal structure shaped like a cross, topped by a dome.