The Harbour Baths are located north of Arcadian Street in the bath-gymnasium complex. They were part of the gymnasium erected in the time of Domitian and devoted to the goddess Artemus and the emperor Antonius Pius. It has also been called the Theater Baths because of the gymnasium’s close proximity to the theatre. It was reconstructed after earthquake in 262 A.D and finally completed in the 4th century A.D.

The main entrance was off of a monumental courtyard off of the Commercial Agora. Opposite the entrance was an exedra decorated with statues. A pool was erected in front of the exedra which visitors could enter from the bath. Three sides of the structure were enclosed. The building had several mosaics and reliefs of a Monument of Parth. Most of these materials were reused

The atrium had a three-naved plan with serrated sections by bricks pillars at the outer walls. The middle section of the bath had a frigidarium, dressing rooms, and relaxation areas. There was a tepid pool that would be accessed either from the frigidarium or from an entrance off the main chamber. Attached to this section of the bath were chambers that would have been used for ball games, boxing, gymnastics, body care and massage. The hot portion of the bath had large Windows and six hot water polls.

The excavation of the gymnasium is incomplete, but parts of the baths have been uncovered. Archaeologists have discovered a pool in the frigidarium with the statue of the god of the River Kaistros. Water would have poured from the amphora the god rests on into the cold water pool.  The complex also had a Hall of Emperors with mosaic decorated floors and statues of the emperors. These statues are now on display in the Izmir Archaeological Museum.