The Theatre of Marcellus is an ancient open-air theatre in Rome, Italy, built in the closing years of the Roman Republic. Space for the theatre was cleared by Julius Caesar, who was murdered before its construction could begin; the theatre was formally inaugurated in 12 BC by Augustus, who named it after his nephew Marcus Claudius Marcellus who had died in 23 BC.
The theatre fell out of use in the early 4th century and the structure served as a quarry, as did many other of the monumental buildings of Imperial Rome. In the Early Middle Ages the theatre was used as a fortress of the roman family of Faffo or Fabi and then at the end of the 11th century (when it was known as templum Marcelli), by Pier Leoni and later his heirs (the Pierleoni). This saved the complex from further destruction. The Savelli held it in the 13th century.
In the 16th century, the residence of the Orsini, designed by Baldassare Peruzzi, was built atop the ruins of the ancient theatre. In the 17th century, the English architect Sir Christopher Wren explicitly acknowledged that his design for the Sheldonian Theatre in Oxford was influenced by Serlio's engraving of the Theatre of Marcellus.