By the Gods!

 The spectacular setting of the chariot race in BEN-HUR (1959)

This shot is a combination set and matte painting. Everything in the middle, including the people in the foreground, are real. The rest is an elaborate matte painting. The big statues in the centre were real. Some of them still exist and can be found somewhere at Cinecittà. The entire scene, from pre-production to the time before they shot it took over a year to prepare. They had to find and train the the horses, the riders, etc. They had to excavate a quarry for the race track. And this is before they actually started filming. The filming of the scene itself took several weeks spread over several months. They were able to find thousands of extras because the economy in Italy was so bad and many people were willing to work for some extra cash. It's one of the most elaborate and complex scenes ever filmed.