I saw a vid about the coliseum that said the portion of the perimeter walls that still exist are founded on bedrock and the portion that is missing was built on fill and fell during earthquakes.
Still, not bad for 1950 years of age, and missing 2/3rds of its original materials. I doubt any current stadium will have such an existence. The Flavian dynasty consisted of just three emperors, and lasted about 27 years. They really got things done back then.