Theater is the most magnificent building of Side and dates back to 2nd century AD. Its back was built in a way to face the Mediterranean Sea.
Although theater is a monument of Roman period, the section reserved for the spectators was made wider than a semi-circle, as in the Hellenistic theaters. It was not possible to take advantage of leaning the theater against a hill in accordance with the traditions since the land on which the city of Side was founded is plain and it was necessary to perform a large construction work.
On a hill of low altitude only the lower half of the cavea could be placed. The cavea with a seating capacity of 16.000 persons had a diameter of 120 m. This structure has 2 floors.
The lower floor includes a semi circular gallery and it is covered with an extended archway placed on wide columns connected with wide arches. Some of the openings between these wide columns open to either a shop or an inner gallery or other covered places used for other purposes.
The walking path dividing the cavea into two, there were passages leading from these inner galleries directly to 3,5 m wide diazoma. The spectators entered through these gates to a diazoma and at the lower section of the theater reserved for them descended to take their seats.
From the diazoma it was not possible to reach the upper seating section of cavea. At the upper part the spectators had to first ascend the internal stairways connecting the lower galleries to the other galleries. Respectively Caveaís upper and lower section have 29 and 22 rows of seats. Since it also hosted the shows performed with wild animals and gladiators in Roman period in addition to theater shows, meetings and festivities, the orchestra of the structure was surrounded with a 1,85 m. high wall in order to protect the spectators.
In the period of Christianity the theater was also used as open theater. For this purpose to the head of cavea two small chapels were added.
The stage building of theater had three floors ( 21m ) with its side turned towards the spectators being made of granite and marble and being decorated with overlapped column pairs and the niches between these, also the statues placed inside these niches. The upper row of columns is in Korinth style, while the lower roe of columns exhibits Ion sytle. On the smooth surfaces between the floors there are friezes.
By five gates it is possible to ascend from the stage building to the orchestra. On the doors of some of the rooms on the lower floor the presence of iron railings leads to the opinion that these were the cages of animals or gladiators. There are passages leading from commercial agora to the lower floor. On the upper floor rooms were dedicated to the use of the artists.
The theater building was made an important element of this defense system and the gates opening from the stage section to the agora was closed by laying bricks in the period when the area occupied by the city was decreased and the intermediate city walls were built for this purpose.