The Temple of Neptune was erected on the Poreč forum in the 1st century. It is thought to be the biggest in Istria, although only a portion of its walls and the foundations have been preserved.
During the Antiquity, Poreč as well as all Roman towns, had a forum, the main town square known today as Marafor, and a Capitoline temple facing it. It was believed that the temple was dedicated to God Mars in light of interpreting the Marafor as the Martis forum i.e. the forum of Mars. To the north-west, also in the near vicinity of the former forum, are the remains of the Large Temple dedicated to Neptune, the god of the sea. There are some who interpret the remains as a holy ground surrounding the Capitoline from three sides. The temple, dated to the 1st century, is the biggest in Istria in spite of only a portion of its wall and foundations being preserved.
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.