This is where the Olympic Games of 1896 were held.
The stadium was first built in ancient times and was remade in marble in 329 BC. By 140 AD was mostly as you see it today, with capacity over 50.000 people.
Unfortunately, wars, uncivilized conquerors, raging enemies and (eventually) time almost completely destroyed it. It was remade once more in modern times to host the 1896 Olympics.
In the 2004 Olympic Games, the Panathinaiko Stadium hosted the archery competition, and served as the finish site for the men's and women's Marathon races.
Panathinaiko Stadium in Wikipedia