The (Roman) theatre of Sagalassos was built in the 2nd century AD. Like almost all Greek/Roman theatres it leans with its cavea on a mountain slope. Especially the western area of the theater was built with vaulted chambers of masonry. Here were the main entrances to the spectator stands. The theatre as well as the whole city of Sagalassos was repeatedly affected by devastating earthquakes. After an earthquake in the 7th century, the city was largely abandoned.

Sagalassos was founded in Hellenistic times and abandoned after a severe earthquake in the early 7th century A.D. during the late antique-early Byzantine epoch. Apparently, the ruined city remained untouched and almost unplundered until the present day, although fragments of columns, buildings and clay fragments signal to the untrained eye an extensive, in its bloom very prosperous ancient city.

When Alexander the Great conquered Sagalassus on his way to Persia in 333 B.C., it was already one of the wealthiest cities in Pisidia. Several thousand inhabitants may have inhabited the city. After Alexander's death, the region became one of the territories of Antigonos I Monophthalmos (321 to 301 BC), possibly Lysimachus (301 to 281 BC), the Seleucids of Syria (281 to 189 BC) and the Attalids of Pergamum (189 to 133 BC). Archaeological findings show that the Hellenistic culture was quickly adopted by the local population.

In the Roman Empire, Sagalassos became one of the most important urban settlements in Pisidia, where a striking discrepancy can be observed between the presumably small number of inhabitants (according to previous knowledge probably well under 10,000 people) and the splendour and size of the public buildings.

Earthquakes repeatedly devastated the city, in particular in 518, but above all an epidemic (the Justinian plague) around 542 also affected Sagalassos and probably killed about half of the population. Once again the place could recover. Persian raids then threatened the town around 620, and after another earthquake, which destroyed the town again at the latest in the middle of the 7th century, it was largely abandoned. The simple people may have populated the valley again. Excavations only revealed signs of a fortified monastery, possibly a religious community destroyed in the 12th century. Sagalassos disappeared from all records and was forgotten. In the following centuries debris and sediments covered the ruins of Sagalassos and because of its location it was not plundered in any significant way.

Around 400 A.D. Sagalassos was fortified, probably a reaction to the tense situation of the empire at that time; nevertheless the place was still important and prosperous during the whole late antiquity; also generous private houses were still built in the 6th century.