The gymnasium, a large structure built near the northern wall to the southwest of the northern city gate, has a rectangular plan facing north-south. In 1977, when the excavations at Stratonikeia began, this is one of the areas where work was carried. Excavations until now have revealed sections on the north side. The north side, the narrow façade is 105 m wide. The total length of the building is estimated to be 267 m. Hence it is the largest known gymnasium in antiquity.
The archaeological and epigraphic finds indicate that the gymnasium was built in the 2nd quarter of the 2nd century B.C. and during the Augustan and Antonine periods new arrangements and reconstruction were made.