The Church of St. Polyeuctus was an ancient Byzantine church in Constantinople (now Istanbul) built by the noblewoman Anicia Juliana between 524 and 527 and dedicated to Saint Polyeuctus. Intended as an assertion of Juliana's own imperial lineage, it was a lavishly decorated building, and the largest church of the city before the construction of the Hagia Sophia. It introduced the large-scale use of Sassanid Persian decorative elements, and may have inaugurated the new architectural type of domed basilica, perfected in the later Hagia Sophia.
Little is known of the church's history after its construction. The building survived until the 11th century, after which it fell into decay, while several architectural elements were removed and reused in Constantinople and other cities. After being built over in the Ottoman period, the site of the church was rediscovered during excavations in the 1960s. The area, directly opposite the Istanbul Metropolitan Municipality City Hall, is now a preserved archaeological site open to visitors, although the sculptures have been removed to the Istanbul Archaeological Museum.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.