The Library of Celsus was a reading room built over a grave. Tiberius Julius Aquila Polemaeanus, a Roman consul, commissioned it in the 110s CE in honour of his father, Tiberius Julius Celsus Polemaeanus, once governor of the province of Asia. Celsus lies in a decorated marble sarcophagus in a crypt beneath the apse. Burial inside a Roman city was rare, so the tomb was a mark of rank.

Celsus paid for the reading as well as the room. An inscription records his legacy of 25,000 denarii for the collection, thought to have reached around 12,000 scrolls. Only Alexandria and Pergamum had larger libraries in the Greco-Roman world. The rolls sat in niches with double walls, probably against damp and heat. Readers used them on the spot. Copies were rare and slow to make, so borrowing would not have been allowed.

The façade was built to look bigger than it is. Its columns differ in length, yet from the street they read as a matching set, and the front seems grander for it. Four statues of virtues stood in the lower niches: Wisdom, Knowledge, Intelligence and Excellence. The figures there today are not the originals.

Fire gutted the interior in 262 CE, after an earthquake or a Gothic raid. Unlike the clay of the Library of Ashurbanipal, papyrus did not survive the flames. An earthquake in the 10th or 11th century brought the front down too. The archaeologist Volker Michael Strocka re-erected it between 1970 and 1978 from fragments excavated in 1903 and 1904. Some pieces had gone to museums in Vienna and Istanbul, so copies fill the gaps. Behind the façade, the building is still a ruin.