The Temple of Olympian Zeus (or Olympieio), one of the most famous archaeological sites in Athens, has been a ruin almost since it was built. Construction began in the 6th century BC., set out to build the greatest temple in the world, but it was not actually finished until about the 2nd century AD. (over 600 years late!) by the Roman emperor Hadrian. By then it was the largest temple in Greece, bigger than the Parthenon, as it was consisted of 104 pillars. In the 3rd century AD it was looted by barbarians and its glory days were over. Since then it has slowly fallen into ruin.
An interesting note in the history of the temple of Zeus is that Hadrian, upon dedicating the temple to Zeus, erected two large statues in the centre of the building. Both were large and one depicted Zeus, the other one Hadrian himself.
The Temple of Zeus in Athens is located near the centre of the city, just about a quarter of a mile to the southeast of the Acropolis, and within a quarter mile south of Syntagma Square and the Parliament Building.