Tinnumburg is the best preserved of the three ancient ring forts in Sylt. The fort was built around the birth of Christ. The rampart has a diameter of 120 meters. The wall is up to seven meters high and has a circumference of about 440 meters. The castle had at least two gates (east and south).
Excavations in 1870, 1948 and 1976 provided evidence that the Tinnumburg was built in the style of early Roman Empire round ramparts on the North Frisian islands. The excavations have shown that this is a Germanic site of worship. The fort was in use again in the 8th to 10th centuries.
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.