Hadrian's Arch, also known as Hadrian's Gate, is an imposing structure similar to a Roman triumphal arch located on an ancient road connecting the center of Athens with the complex to the east of the city, including the Temple of Olympian Zeus. It is suggested that it may have been built to commemorate the arrival of the Roman emperor Hadrian, although who was responsible for its construction and the exact purpose, such as dividing the city, are uncertain. Built 325 m from the Acropolis, it uses marble from Mount Pentelicus, although of inferior quality to that of the Parthenon.

With a length of 18 meters, height of 13.5 meters and depth of 2.3 meters, the arch presents a symmetrical design both in front and on the sides. Built without cement, it uses solid marble and clamps to join the blocks. The lower level, with a span of 6.5 meters, has pilasters with Corinthian capitals. The upper level has Corinthian columns, pilasters and a triangular pediment. Although it differs from Roman triumphal arches, the upper level has a sophisticated design that does not allow for the addition of heavy ornamentation. It is proposed that statues of Theseus and Hadrian may have been at the top, but evidence is limited. Although the lower level has been studied, a full investigation, including excavation of the foundations, is still pending.