- The Temple of Poseidon / Neptune (also known as the second Temple of Hera) was built around 460-450 BC.- Paestum was a major ancient Greek city on the coast of the Tyrrhenian Sea in Magna Graecia (southern Italy). Paestum was founded as the city of 鈥楶oseidonia' by the Greek colonists in about 600 BC.The ruins of Paestum are famous for their three ancient Greek temples in the Doric order; dating from about 550 to 450 BC.Italy. 2021.