The Greek and Roman empires most certainly have not existed the entire time, and you're talking about extremely long timelines. Even if there was a sitting Roman emperor for the past 2500 years and the entire period had not seen a single invasion succeed, you're talking about a maximum 50 year reign for each emperor. That's 50 lifetimes. Now consider that many rulers during that period only lasted a few months and you might start to see the problem.

Try to find a building in New York City that's older than 100 years. Most of them just get torn down for being old and decrepit, and that's with our current engineering technology, using machines and materials that could never have existed in ancient times. Throw in regular earthquakes and other natural disasters that cause further damage.

Thats pretty much what happened to the Roman Colluseum. Several political leaders considered it a ruin worth only it's scrap materials, and used that stone for other building projects to save money. It certainly wasn't usable for its original purpose even 1500 years ago.

Academia works differently though. Even in America they have sabbaticals for years at a time.

The CPU is a general-purpose computer. It's strength lies in being able to do any kind of calculation. A GPU is a specialized computer that's optimised for the specific task of rendering 3D graphics, and does its job much faster as a result.