If someone mentions about the Egyptian Pyramids, you'll usually envision a big mountain-like structure that is made up of brown heaps of stone with a rough outline standing in the middle of the desert. But did you know that in 2500 BC, when pyramids were first constructed, their color was paper white and they're very smooth like glass? On top, you would also find a gold-colored capstone that shined under the sun. Indeed, the Pyramids were a breathtaking spectacle at that time. However, when the Arabs invaded Egypt in 500 AD, the pyramids' smooth limestone was stripped off to build a huge portion of Cairo. Most of Cairo's palaces and mosques consist of the pyramids' ancient stones. It's quite disappointing but it's true.