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:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.