The Library of Celsus, whose façade has been carefully reconstructed from all original pieces, was built in honor of Tiberius Julius Celsus Polemaeanus (completed in 135 C.E.) by Celsus’ son, Gaius Julius Aquila (consul, 110 C.E.). Celsus had been consul in 92 C.E., governor of Asia in 115 C.E., and a wealthy and popular local citizen.

The Library of Celsus was designed with an exaggerated entrance — so as to enhance its perceived size, speculate many historians — the building faces east so that the reading rooms could make best use of the morning light.

The library was built to store 12,000 scrolls and to serve as a monumental tomb for Celsus. It was unusual to be buried within a library or even within city limits, so this was a special honor for Celsus.

The building is important as one of few remaining examples of an ancient Roman-influenced library. It also shows that public libraries were built not only in Rome itself but throughout the Roman Empire. In a massive restoration which is considered to be very true to the historic building, the front façade was rebuilt and now serves as a prime example of Roman public architecture. (The Library of Celsus may serve as a model for other, less well preserved, libraries elsewhere in the Empire, for it is possible that literary collections were housed in other Roman cities for the benefit of students as well as traveling Romans. Such libraries may also have housed collections of local documents of interest if they were not destroyed during the Roman conquest.

This type of facade with inset frames and niches for statues is similar to that found in ancient Greek theaters (the stage building behind the orchestra, or skene) and is thus characterized as "scenographic".

The building's other sides are irrelevant architecturally because the library was flanked by buildings.

The inside of the building, not fully restored, was a single rectangular room (55 feet wide by 36 feet (11 m) long) with a central apse framed by a large arch at the far wall. A statue of Celsus or of Athena, goddess of wisdom, stood in the apse, and Celsus’ tomb lay directly below in a vaulted chamber. Along the other three sides were rectangular recesses that held cupboards and shelves for the 12,000 scrolls. Celsus was said to have left a legacy of 25,000 denarii to pay for the library's reading material.

The style of the library, with its ornate, balanced, well-planned façade, reflects the Greek influence on Roman architecture. The building materials, brick, concrete, and mortared rubble, signify the new materials that came into use in the Roman Empire around the 2nd century C.E.

The building's façade was depicted on the reverse of the 20 new lira banknote of 2005-2009. The extent of restoration is nothing less than amazing. Ephesus popularity with tourists is well deserved and for most it will be a highlight of their holiday in Turkey.