In form, the complex resembles the Roman Forum-style and is made up of an immense, almost square, walled enclosure, with entrance on the west. The walls on the north, south, and east were made of porous limestone, while the western wall was built of Pentelic marble. The western side also had a row of Corinthian columns (made from marble from Karystos in southern Evia Island) on the facade, on both sides of the main entrance. Inside, it became an open-air courtyard – with a central, decorative, oblong pool and garden – encircled by columns created from marble imported from Phrygia (no longer preserved). At the eastern end of the colonnade were successions of rooms (called oikemata by Pausanias) that housed the "library" – where rolls of papyrus books were warehoused and adjoining galleries served as reading rooms and lecture halls.

Named the, "Library", of Hadrian since the early 19th Century, it was notably more important than just that. Archaeologists agree that the architectural structure gave the people of Athens a new, multi-purpose, public square and cultural epicenter.

The complex was extremely damaged by the Herculian invasion of 267 A.D. and repaired by the prefect, Herculius, in 407-412 A.D. By the time of the Byzantine era, three churches were erected and still preserved at the location. The remains are preserved and include a tetraconch (5th Century A.D.), a three-aisled basilica (7th Century A.D.), and a modest cathedral (12th Century A.D.) – the latter of which was the first cathedral of Athens, named «Megali Panagia». During the same time frame, Agios Asomatos sta Skalia church, was constructed against the north facade, but was not able to be preserved.