Considering that they are 4500 years old, not anytime soon. Even without maintenance, they would last some more millenia. But if you look at the difference between how they look now and how they used to look, they have suffered quite a bit. Only because they are the most robust structure ever built by man, doesn't mean we should just watch slowly decay. Especially while most of their structure is still close to original, it would be a good time to restore them.
Imagine, if for example the acropolis in Athens would have been kept in original state vs. mostly having decayed. All those wonders of the past we decided to keep, we should preserve, while it is still possible.
To be clear, the Acropolis did not “decay”. It was blown up by the Venetians when they fired on the Parthenon, which at the time was used to store gunpowder.
Thanks, I didn't know that. But the world is full of ruins of great old places, which we try to preserve today, but had not been kept in shape when they were still close to their origininal state. I think old churches are one of the few exceptions.
"Beeldenstorm in Dutch (roughly "statue storm"), and Bildersturm in German ("image/statue storm") are terms used for outbreaks of destruction of religious images that occurred in Europe in the 16th century, known in English as the Great Iconoclasm or Iconoclastic Fury. During these spates of iconoclasm, Catholic art and many forms of church fittings and decoration were destroyed in unofficial or mob actions by Calvinist Protestant crowds as part of the Protestant Reformation. Most of the destruction was of art in churches and public places."
Sure, a lot of churches also got destroyed. Yet, a lot of churches are in a remarkably good state of preservation. They are not the only preserved buildings, but the most obvious ones. There are also a few roman aquaeducts preserved, like the one in Nimes, France. And if I am not mistaken, some of the water delivery to todays Rome still uses partially roman aquaeducts. Also, the Pantheon in Rome is in a remarkably great state.
The sad thing about the Parthenon (and the Acropolis in general) was that it had been well preserved until then, albeit with changes. It had successively been a church and a mosque. Unfortunately, the Acropolis was also the most defensible position in Athens, so it was (since its inception) a strategic outpost as well. :-(
Acid rain can't be good for limestone. At the size of the pyramids, though, I'm not sure if the effects would be noticeable at all. It also doesn't rain much in the desert.
