The Roman theatre of Cádiz is an ancient structure discovered in 1980. The theatre, which was likely built during the 1st century BC and was one of the largest ever built in the Roman empire, was abandoned in the 4th century and, in the 13th century, a fortress was built on its ruins by order of King Alfonso X of Castile.
The theatre featured a cavea with a diameter of more than 120 meters, and could house some 10,000 spectators. The theatre was one of the few Roman structures of ancient Hispania mentioned by classical authors, including Cicero and Strabo. Excavations in the site have also found remains of a quarter dating to the taifa period, Almohad houses and 17th century pits.
References:The ancient Argos Theater was built in 320 BC. and is located in Argos, Greece against Larissa Hill. Nearby from this site is Agora, Roman Odeon, and the Baths of Argos. The theater is one of the largest architectural developments in Greece and was renovated in ca 120 AD.
The Hellenistic theater at Argos is cut into the hillside of the Larisa, with 90 steps up a steep incline, forming a narrow rectilinear cavea. Among the largest theaters in Greece, it held about 20,000 spectators and is divided by two landings into three horizontal sections. Staircases further divide the cavea into four cunei, corresponding to the tribes of Argos A high wall was erected to prevent unauthorized access into the theatron and may have helped the acoustics, but it is said the sound quality is still very good today.
Around 120 CE, both theaters were renovated in the Roman style.