The Teatro Romano in Trieste was built in the first century BC and expanded in the second century AD. It had seats for from 3,500 to 6,000 visitors. It was probably built by the Trieste Quinto Petronio Modesto , prosecutor Emperor Trajan.
Over the centuries, the theater was left under the houses that were built above. Considered lost, it was identified in 1814 and unearthed in 1938 during the demolition of this part of the old city. The statues and inscriptions found in the excavations are kept in the San Guisto Castle.
Nowadays Teatro Romano is still occasionally used for outdoor summer shows.
FYI this is not an amphitheater because it is not in the round. It is simply a theater.
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.