Concise Bible Dictionary:

A place built for dramatic and other public entertainments, and for meetings of the people. At the uproar at Ephesus they rushed into the theater (Acts 19:29,31). The word is θέατρον, and is translated “spectacle” in 1 Corinthians 4:9; the apostles were gazed upon both by angels and by men.
Roman Theater – Caesarea Maritima