Temple of Olympian Zeus

It took 638 years to finish. Let that sink in. The Temple of Olympian Zeus is the longest construction project in the ancient world — begun around 520 BC by the Athenian tyrant Peisistratos and his sons, abandoned when democracy replaced tyranny (the Athenians considered the project an act of hubris), picked up briefly by a Seleucid king in 174 BC, and finally completed by the Roman Emperor Hadrian in 132 AD. By the time it was done, the original architects had been dead for over half a millennium.

When finished, it was the largest temple in Greece. One hundred and four Corinthian columns stood 17 meters tall — taller than a five-story building — arranged in a double colonnade that stretched across a massive footprint. Inside sat a chryselephantine statue of Zeus so enormous that Hadrian placed a matching statue of himself right next to it, because modesty wasn't really a Roman virtue. The temple's glory lasted barely a century: Germanic Heruli raiders sacked it in 267 AD, and it was never restored.

Today only 15 columns remain standing — 13 in the southeast corner and 2 in the southwest. A sixteenth column lies where it fell during a storm in 1852, its drums stacked like toppled coins. But even as ruins, the scale is staggering. Each column drum weighs about 5.5 tons, and standing among them you get a visceral sense of the building's original enormity.

The temple sits in a fenced archaeological zone alongside the much smaller but equally fascinating ruins of Roman baths, houses, and a basilica — all visible from the street but somehow overlooked by most tourists rushing between the Acropolis and Plaka.