The ancient Agora of Argos started to be organized during the 5th century BC. in the south of the city, on the crossroads from the Heraion of Argos, Corinth and Tegea. The architectural programme was completed at the end of the 4th century BC. During the Classical and the Hellenistic periods, the Agora was surrounded by porticos and buildings which can hardly be distinguished at present under the later architectural phases.
During the Roman times, many of the existing buildings were altered in shape and function, mostly into shops and fountains when, in the 2d and 3d century A.D. a general remodeling of the site took place. Later, during the 4th century A.D., a last monument of Paganism was built, a hearth surrounded by boundary steles from the enclosure (peribolos) of an 'heroon' of the Archaic period dedicated to the 'Seven against Thebes'. The invasion of the Goths, in 395-396 A.D. accelerated the destruction and the disappearance of the monuments of the Agora.
References:The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.