The Arch of Hadrian is a monumental gateway resembling – in some respects – a Roman triumphal arch. It spanned an ancient road from the center of Athens, to the complex of structures on the eastern side of the city that included the Temple of Olympian Zeus. It has been proposed that the arch was built to celebrate the adventus (arrival) of the Roman Emperor Hadrian and to honor him for his many benefactions to the city, on the occasion of the dedication of the nearby temple complex in 131 or 132 AD.
It is not certain who commissioned the arch, although it is probable that the citizens of Athens or another Greek group were responsible for its construction and design. There were two inscriptions on the arch, facing in opposite directions, naming both Theseus and Hadrian as founders of Athens. While it is clear that the inscriptions honor Hadrian, it is uncertain whether they refer to the city as a whole or to the city in two parts: one old and one new. The early idea, however, that the arch marked the line of the ancient city wall, and thus the division between the old and the new regions of the city, has been shown to be false by further excavation.
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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.