Temple of Olympian Zeus, Athens — begun in the 6th century BC and finally completed by the Emperor Hadrian in 131 AD, making it one of the longest construction projects in ancient history at over 650 years. Of its original 104 columns, 15 still stand; a 16th fell in a storm in 1852 and lies exactly where it landed.
Julian Lupyan, CC0, via Wikimedia Commons
