At the edge of the Ancient Agora of Athens is the temple of Hephaestus, best known as Thissio. The temple was built between 450 and 420 BC in unknown architect plans and exemplifies the Doric order. It is also made from the famous Pentelic marble and the temple has a total of 34 columns (6 on the front and back and 13 on the sides). The fronts of the temple were decorated with themes from Greek mythology, including the labors of Hercules and the Athenian hero's Theseus (of which it is probable that it got the name Theseion-Thisio).

The Temple of Hephaestus is one of the best preserved temples in the world and to this probably contributed greatly the fact that it was converted into a Christian church (St George) in the 7th century AD, thereby avoiding total destruction. It is worth-noting that because during the Ottoman rule the operation of the church was prohibited (except once a year on the feast of the saint), the locals called it "Saint George Akamati".

In 1834 the welcome ceremony of the first king of Greece, Otto, took place in Thissio.