The Temple of Olympian Zeus (Ναὸς τοῦ Ὀλυμπίου Διός) was intended to be the largest temple in the ancient world. Its constructions had been started in 6th century BC and completed in the 2nd century AD. But it was significantly damaged by the barbarians in the 3rd century AD and never recovered again. The temple is built of marble and its columns are 17 m height and 2 m in diameter.
Later its stones were used to build another buildings in Athens but the remained part is still amazing.