During the Hellenistic Period an intensive building program resulted in an enormous expansion of the settled area. On the other hand, political instability and conflicts during the Period of the Diadochoi resulted in a rather insecure setting.

As a result of these security concerns during the Hellenistic Period, a new defensive line on the northern slope and two separate defensive lines on the southern slope of the city were built. City’s total area enclosed by defense lines was reached to 23,2 hectares in the Hellenistic period. Two main political situations determined the construction of the Hellenistic defensive lines in Aigai. Firstly, several battles are reported for supremacy between the Kingdom of Pergamon and the Seleucids from the short-lived occupation of the area by Achaeus in 223-218 BCE until the Battle of Magnesia in 190 BCE. It is believed that the defence of Pergamon was reinforced during the peaceful Period of Eumenes II (179-174 BCE), succeeding the previous unsteady period. Perhaps the fortification walls of Aigai were repaired, extended, and reinforced during the same years. Another important incident was the destruction of Aigai during the war between Attalus II and Prusias I in 156-154 BCE. In 154 BCE Prusias II was forced to pay compensation of one hundred talents to the cities he had damaged.

The costly monumental public buildings of Aigai, such as the Bouleuterion, the Agora Building, the Stoai of the Agora, the Theater, the Gymnasion, and the Stoai of the Sanctuary of Athena might have been reconstructed, constructed, or finished immediately after the middle of the 2nd century BCE. Reparation, reinforcement, and enlargements of the last phase must have been also applied to the Hellenistic fortification walls of the city at the same period. The length of the Hellenistic wall on the northern slope of Aigai was around 630 m Today about 500 m of this wall are visible. The area enclosed by the fortification walls outside the acropolis covers approximately three hectares. A gate is located at the point where the ancient road leading to the city through the northern necropolis reaches the fortification wall. This gate is integrated into the course of the wall and shows no overlapping form as do the older gates of the city. It was, however, protected by the adjacent rectangular tower with its slanted northern façade.

The eastern and western endings of the Hellenistic fortification walls forming defense line on the southern slope were leaned on the diateichisma. With the addition of the outer wall on the south, it is felt that acropolis and the area enclosed by diateichisma gained a concept of the upper city and the area enclosed by outer northern and southern walls as the lower city. The length of the outer wall on south, which can be followed today, is 430 m and its length in antiquity was ca. 865 m. The area enclosed by the wall varying between 1 and 2,10 m in thickness, is ca. 7,3 hectares. On the parts where the wall is not preserved, its course is indicated by foundation beddings cut into the bedrock. Five circular planned towers were built to support the defense line. Two of them named K2 and K3 support an arched gate on the southern edge of the southern slope. The overlapping gate on the northwestsoutheast axis should have double towers and a courtyard. The southern and northern necropoleis expanded to the outer fortification walls in parallel with the city’s expansion due to reconstruction programs held in the Hellenistic Period. The dominant preference of Doric order on public and religious architecture of Aigai must have been the result of Pergamon’s hegemony in the 2nd century BCE. The city did not lose its importance during the Roman Period and the plan of the city was not changed much. Some of the buildings were renovated and some were rebuilt after the 17 CE earthquake.

The most important informations was obtained from the North Bath and Insula 1 sector located on the northeast of the Acropolis. The area along the northeastern side of the main street reaches the city through the Gate of Agora Street, located to the south of the North Bath built in the 2nd century CE, is named as Insula 1. The area, where 28 workshops and 6 cisterns were unearthed so far, fell into disuse due to the abandonment of the city in the third quarter of 3th century CE. Archaeo logical data indicate that the area was housing several branches of industrial production. A bath structure was added next to Gymnasion in the Roman Period. The Hellenistic theater was enlarged; a vomitorium and a decorated stage building were added.