The natural extension of the ancient Greek Agora, built in the second half of the 1st century BC, with donations from Julius Caesar and Augustus.

The Agora building (111 x 98 m) had a large rectangular atrium surrounded by stoas, shops, and storerooms. The Ionic peristyle that survives dates from the 2nd century AD. The best preserved sections of the colonnades stand on the southern and eastern sides. The west entrance, known as the Gate of Athena Archegetis is in excellent condition.

On the south sides, the remains of a fountain and a stairway that presumably led to an upper floor (maybe to the Agoranomion which supervised the market) are visible. A second propylaeum – of the Ionic order- and a row of shops mark the east side while, on the north, the remains of the Vespasianae (public latrines; 1st century AD) can be seen.

The Roman Agora became even more significant after the terrible destruction of Athens by the Heruli (267 AD), after which many activities of the Ancient Agora were transferred to the Roman Agora.