The Theodosian Walls are the fortifications of Constantinople, capital of the Byzantine Empire, which were first built during the reign of Theodosius II (408-450 CE). Sometimes known as the Theodosian Long Walls, they built upon and extended earlier fortifications so that the city became impregnable to enemy sieges for 800 years. The fortifications were the largest and strongest ever built in either the ancient or medieval worlds. Resisting attacks and earthquakes over the centuries, the walls were particularly tested by Bulgar and Arab forces who sometimes laid siege to the city for years at a time. Sections of the walls can still be seen today in modern Istanbul and are the city's most impressive surviving monuments from Late Antiquity.
Although the city had benefitted from previous emperors building fortifications, especially Constantine I when he moved his capital from Rome to the east, it is Emperor Theodosius II who is most associated with Constantinople's famous city walls. It was, though, Theodosius I (r. 379-395 CE) who began the project of improving the capital's defense's by building the Golden Gate of Constantinople in November 391 CE. The massive gate was over 12 meter's high, had three arches, and a tower either side. It was entirely built of marble and decorated with statues and was topped with a sculpture of a chariot pulled by four elephants. The Golden Gate probably marked the start of triumphal processions which ended in the Hippodrome. Two decades later, Theodosius II was alarmed at the recent fall of Rome to the Goths in 410 CE and set about building a massive line of triple fortification walls to ensure Constantinople never followed the same fate. The man credited with supervising their construction is Theodosius' Praetorian Prefect Anthemis. The walls extended across the peninsula from the shores of the Sea of Marmara to the Golden Horn, eventually being fully completed in 439 CE and stretching some 6.5 kilometers. They expanded the enclosed area of the city by 5 square kilometers.
