What geographical change over time do the sites of the major monuments show

The correct answer is - erosion.

The sites of the major monuments over time show signs of erosion. As all these sites are made out of natural materials they are not prone to the effects of the erosion. Little by little, over time, they have small parts of them removed with this natural process, thus changing their initial forma and shape, but also threatening to totally destroy them. The erosion has increased in the past century because of the acid rains as they have very high corrosive power.

Because of this, lot of sites of major monuments have been restored, new layers are added, for both making them look as they initially did, and for bigger protection of the natural elements.