When we look at the great monuments of past civilizations, I used to wonder what made one monument last while others disappear from the earth altogether. The answer I think is two-fold. First is the old maxim of "Location, Location, Location". Earth is a very violent planet. Just halfway through 2008 we've already seen a major earthquake in central China, a "500-year" flood in the midwestern United States, and the rebirth of a long dormant volcano in Chile. Historically, an earthquake destroyed the Colossus of Rhodes, a sinkhole swallowed the Lost City of Ubar, and we will never know what all was lost when the Santorini/Thera eruption rocked the Minoan Empire. So many of the monuments still standing are that way because they are in relatively quiet neighborhoods geologically and climatically.
The second contributor to lasting monuments is their usefulness across cultural and political lines. Everyone has heard the urban legend of Napoleon's cannoneers blowing off the nose of the Sphinx (in reality a religious fanatic was executed for that crime in the 14th Century). Regimes change, and new regimes destroy the monuments of old regimes. Religions change, and new religions destroy the idols of the old. But some things never change: the human needs for food, water, and exotic silks from the Far East. And it is my belief that monuments which serve a function for agriculture, navigation, and trade are the most lasting of monuments due to their ongoing utility.
