The Temple of Isthmia is an ancient Greek temple on the Isthmus of Corinth dedicated to the god Poseidon and built in the Archaic Period.
It is about 16 kilometers (9.9 mi) east of ancient Corinth. It appears to have been constructed in the seventh century BC though was later destroyed in 470 BC and rebuilt as the Temple of Poseidon at Isthmia in c. 440 BC during the Classical period.
There are two other significant temples to Poseidon, one on the Cape of Sounion near Athens, and a third at Paestum, Italy.
The site of the Temple of Poseidon at Isthmia was one of great activity up until the third century AD. It was the last location of one of the four Pan-Hellenic Games from the sixth century (around 581 BC) to be found, and had numerous buildings constructed in its vicinity. These ranged from Roman baths to a theatre and most importantly two temples.
The Archaic temple was the first erected and was destroyed by fire in 470 BC; the site of the temple was then rebuilt upon, resulting in a larger temple constructed directly on top of the Archaic in the Classical period, which was also destroyed by fire, this time in 390 BC.
Excavations of the site were conducted in both the original 1952 excavations, and again in 1989. The latter excavations helped to uncover evidence relating to all the areas of development of Isthmia from the Bronze Age to the Roman period, but in particular focused on the Archaic temple, partly because this is the most complete of the buildings found at the site despite being one of the oldest.