It's not often you see a structure that uses only one construction material, in this case, millions and millions of cubic yards of concrete.  It's also quite unusual to see modern men building structures designed to last for thousands of years. Most buildings today are designed without any thought to more than 30 years out.

back-1-2-3-4-5-6-7-8-9-10-11-12-13-14-15-16-17-18-19-20-21-22-next