The Temple of Hephaestus, also known as the Hephaisteion or earlier as the Theseion, is the best-preserved ancient Greek temple; it remains standing largely as built. It is a Doric peripteral temple, and is located at the north-west side of the Agora of Athens, on top of the Agoraios Kolonos hill. From the 7th century until 1834, it served as the Greek Orthodox church of St. George Akamates. Hephaestus was the patron god of metal working and craftsmanship. There were numerous potters' workshops and metal-working shops in the vicinity of the temple, as befits the temple's honoree.
Archaeological evidence suggests that there was no earlier building on the site except for a small sanctuary that was burned when the Persians occupied Athens in 480 BC. The name Theseion or Temple of Theseus was attributed to the monument under the assumption it housed the remains of the Athenian hero Theseus, brought back to the city from the island of Skyros by Kimon in 475 BC, but refuted after inscriptions from within the temple associated it firmly with Hephaestus. After the battle of Plataea, the Greeks swore never to rebuild their sanctuaries destroyed by the Persians during their invasion of Greece, but to leave them in ruins, as a perpetual reminder of the war. The Athenians directed their funds towards rebuilding their economy and strengthening their influence in the Delian League. When Pericles came to power, he envisioned a grand plan for transforming Athens into the centre of Greek power and culture.
Construction started in 449 BC, and some scholars believe the building not to have been completed for some three decades, funds and workers having been redirected towards the Parthenon. The western frieze was completed between 445-440 BC, while the eastern frieze, the western pediment and several changes in the building's interior are dated by these scholars to 435-430 BC, largely on stylistic grounds. It was only during the Peace of Nicias (421-415 BC) that the roof was completed and the cult images were installed.
The temple was officially inaugurated in 416-415 BC. Many architects have been suggested, but without firm evidence one refers simply to 'The Hephaisteion Master'. The temple is built of marble from the nearby Mt. Penteli, excepting the bottom step of the krepis or platform. The architectural sculpture is in both Pentelic and Parian marble. The dimensions of the temple are 13.708 m north to south and 31.776 m east to west, with six columns on the short east and west sides and thirteen columns along the longer north and south sides (with the four corner columns being counted twice).
The building has a pronaos, a cella housing cult images at the centre of the structure, and an opisthodomos. The alignment of the antae of the pronaos with the third flank columns of the peristyle is a design element unique middle of the 5th century BCE. There is also an inner Doric colonnade with five columns on the north and south side and three across the end (with the corner columns counting twice). The decorative sculptures highlight the extent of mixture of the two styles in the construction of the temple. Both the pronaos and the opisthodomos are decorated with continuous Ionic friezes.