in 323 BC and lasted until the Roman Victory at the Battle of Actium in 31 BC. As Ancient Greece began to change from a culture consisting of ethnic and city-state Greeks to one governed by large monarchies, theatre architecture to include the stage buildings began to experience significant changes. In the 4th century BC, the became a permanent stone structure and the stage was raised off the ground. In surviving examples this stage seems to have been raised by 2.5–4 m above the orchestra, and to have been 2–4 m deep, terminated by the . As the Greek chorus declined in importance compared to a smaller group of main actors, the chorus remained in the orchestra to perform, while the main actors generally performed from the stage on top of the . This important change occurred in the Hellenistic period, between the 3rd and 1st centuries BC. The itself became increasingly elaborate, and was also available as a place for actors to declaim from, so that the performers between them had three levels available. "The roof of the was called the ('god-speaking'), from which one might assume that its primary use was for the advent of deities, either at the start or close of the drama." Most theatres still standing today date from the Hellenistic period. Roman period In Roman theatres, scaenae frons ('facade of the ') is the term for the elaborately decorated stone screens, rising two or three stories, that the had now become. By the 1st century BC, the was as elaborate as its Roman development, which dispensed with the orchestra altogether, leaving a relatively low facade, often decorated, and a wide stage or behind, ending in an elaborate with three or more doors, and sometimes three stories. The evolution of the actor, who assumed an individual part and answered to the chorus (the word for actor, , means 'answerer'), introduced into drama a new form, the alternation of acted scenes, or episodes. The no longer supported painted sets in the Greek manner, but relied for effect on elaborate permanent architectural decoration and consisted of a series of complex stone buildings. To each side there was a . The was the upper floor of the , which might be deepened to give a third stage level, seen through or openings. The interior of the ('building') behind the facade remained normally outside the view of the audience,