How are Rome's monuments still standing?
TL;DR: their concrete was different.<p>> Roman concrete, on the other hand, is a simpler mix of quicklime made from baking and crushing limestone rocks and, most importantly, volcanic rock aggregates of various types, which were abundant in the region surrounding Rome. In contrast to the aggregates used in modern concrete, these volcanic materials used by the Romans are highly reactive and the resulting concrete remains chemically active for centuries after it first hardens.<p>By the way, I don't buy this entirely. Let me tell you why.<p>The Pantheon is mostly stones and bricks, and "some" concrete to keep the bricks together. These large stones are held together by simple force of gravity, very much like the Pyramids in Egypt (~4,000 years old, or double the age of the Colosseum or the Pantheon).<p>I'm not a materials engineer (just a software engineer). Can someone with more knowledge comment on my view?