The theater of Pompey is the first permanent theater in Rome. The construction was planned and financed by the general and consul Gnaeus Pompeius Magnus (106-48 BC). It was situated on southern part of the Campus Marius.
The structure was the first in Rome to be free-standing, not set into a hillside. It was built with concrete foundations from the ground up, with access corridors under the seating.
The stone/masonry edifice with a stage 300 feet wide comprised a large leisure complex where gardens were enclosed with collonade, galleries for rare artworks, and a curia (Senate meeting hall). The semi-circular seating area's facade consisted of three arcades with columns.
Although almost no remains are visible, the theater will always be connected with Julius Caesar, who was killed in the building. More detailed information can be found here.