Though only a few columns remain of the Temple of Olympia Zeus in Athens it does not take much imagination to realize that this was one gigantic temple. Construction began in the 6th century BC during the rule of the Athenian tyrants, who envisaged building the greatest temple in the ancient world, but it was not completed until the reign of the Roman Emperor Hadrian in the 2nd century AD some 638 years after the project had begun.