The Roman Agora, also known as Agora of Caesar and Augustus, is situated in the northern foothills of the Acropolis, east of the Ancient Agora, at the area where open-air trade used to take place. Its construction began in 51 BCE following a donation from Julius Caesar, was paused in 47 BCE and was finally completed by Augustus between the years 19 and 11/10 BCE. The function of the Ancient Agora had already changed, thus, the need to relocate commercial activities had risen. The placement of the new building was determined by the position of the Ancient Agora, approximately 80 metres west of the new site, as well as by the pre-existing road network.

The building, designed to accommodate commercial activities, was innovative, combining Roman architecture with classical tradition. Its dimensions were 111 by 104 metres, it was enclosed, surrounded by a continuous high wall and featured a central colonnaded square. The four Ionic porticos arranged on its sides were not interconnected, while on the southern side, and probably also on the northern one, there was a second, inner colonnade of non-fluted Doric columns. Behind the eastern colonnade, shops were housed, while behind the western one, two elongated spaces were formed, believed to have been used as storage for goods. The two main entrances of the Agora featured monumental gateways (propylaea): to the west a Doric one, the so-called Gate of Athena Archegetis, and to the east an Ionic one, with non-fluted columns. The materials used included limestone and marble from mounts Hymettus and Pentelicus, while many architectural elements were in second use, previously belonging to other buildings that were no longer in use.

Statues of Augustus and other members of the imperial family had been erected at the propylaea and other spots. Drawings and engravings by 18th century travellers depict a statue of Lucius Caesar, grandson of Augustus, on horseback in the western propylon, a statue of Gaius Caesar, brother of Lucius, and a statue of Livia, wife of Augustus. During the excavations of the site, a portrait of Augustus was found, while other portraits of emperors discovered in the surrounding area are believed to have been set up in the Roman Agora. Of great interest are also the inscriptions found at the site. Some of them provide information about the locations of specific merchants inside the Agora or their shops behind the eastern colonnade. In addition, a decree from the time of Hadrian (117-138 CE) with provisions concerning the olive producers has been preserved, suggesting that the Roman Agora was the city’s main marketplace for olive oil.

After the 1st century CE, the road connecting the Ancient with the Roman Agora was paved and porticos with shops were built on both its sides. Shortly afterwards, possibly during the reign of Emperor Hadrian, the central square of the Agora was paved with marble slabs. Due to the intensive use of the area, continuous interventions and repairs were carried out in later periods. When the Heruli raided Athens, in 267 CE, the site does not seem to have suffered major damages, and, after the construction of the Late Roman wall a few years later, the Agora was included within its enclosure and remained in use. A number of scholars argue that, at the time, it housed administrative services. During the 3rd or 4th century CE, a large drainage network was constructed along the inner perimeter of the building, with clay pipes and brick shafts. Later, in the late 7th-early 8th century CE, a basilica was built in the north-east corner of the Agora.