Olympieion: Temple of Olympian Zeus, Athens. Greece.

Dedicated to Zeus, the Temple of Olympian Zeus, also called the Olympieion, was the largest temple in ancient Greece. Though the Parthenon is better preserved, the Temple of Olympian Zeus was an even more monumental structure in its day. The temple dates to the sixth century BC but was not completed until the second century AD by the Emperor Hadrian. In front of the Olympieion, not far from the entrance, stands Hadrian's Arch at the end of Dionysiou Areopagitou.

It's easy to imagine the grand impression this temple made in its complete form. More than a hundred enormous marble columns once supported the grandiose sanctuary. Only 15 columns remain standing, and another surviving column lies on the ground, but the ruins' monumental presence gives a sense of the massive size of the original building. The gigantic structure was a befitting shrine to Zeus, the ancient Greeks' most all-powerful God, known as the King of Gods.