Byzantine emperor Justinian I lays the foundation stone of a new Orthodox Christian basilica in Constantinople – the Hagia Sophia.

The foundation of Constantinople in 330 AD marks the conventional start of the Eastern Roman Empire, which fell to the Ottoman Empire in 1453 AD. Only the emperors who were recognized as legitimate rulers and exercised sovereign authority are included, to the exclusion of junior co-emperors who never attained the status of sole or senior ruler, as well as of the various usurpers or rebels who claimed the imperial title.

Justinian I, also known as Justinian the Great, was Byzantine Roman emperor from 527 to 565.

The Eastern Orthodox Church, officially the Orthodox Catholic Church, and also called the Greek Orthodox Church or simply the Orthodox Church, is one of the three major doctrinal and jurisdictional groups of Christianity, with approximately 230 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops via local synods. The church has no central doctrinal or governmental authority analogous to the pope of the Catholic Church. Nevertheless, the Ecumenical Patriarch of Constantinople is recognised by them as primus inter pares, a title held by the patriarch of Rome prior to 1054. As one of the oldest surviving religious institutions in the world, the Eastern Orthodox Church has played an especially prominent role in the history and culture of Eastern and Southeastern Europe. Since 2018, there has been an ongoing schism between Constantinople and Moscow, with the two not in full communion with each other.

In Ancient Roman architecture, a basilica was a large public building with multiple functions that was typically built alongside the town's forum. The basilica was in the Latin West equivalent to a stoa in the Greek East. The building gave its name to the basilica architectural form.