Hadrian's Library was created by Roman Emperor Hadrian in AD 132 on the north side of the Acropolis of Athens.
The building followed a typical Roman Forum architectural style, having only one entrance with a propylon of Corinthian order, a high surrounding wall with protruding niches (oikoi, exedrae) at its long sides, an inner courtyard surrounded by columns and a decorative oblong pool in the middle.The library was on the eastern side where rolls of papyrus 'books' were kept. Adjoining halls were used as reading rooms, and the corners served as lecture halls.
The library was seriously damaged by the Herulian invasion of 267 and repaired by the prefect Herculius in AD 407-412. During Byzantine times, three churches were built at the site, the remains of which are preserved: a tetraconch (5th century AD), a three-aisled basilica (7th century) and a simple cathedral (12th century), which was the first cathedral of the city.
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.