There are two ancient hill forts in Porvoo, so-called small and big one. There is burial ground in a small hill from the Roman Iron Age (0-400 AD). The items found in excavations reveal that Porvoo river has been a remarkable trading centre already in prehistoric times and local people has had connections to Estonia and Latvia.
The bigger hill fort is one of the largest in Finland. It was used for defensive purposes already in the Viking Age (800-900 AD), but the fortifications date from the late 14th century. Today remains of double walls and dry moat are visible and restored.
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.