Anyone coming down the Nile from Nubia would sail beside it. It's grandeur was meant to intimidate and awe.  It was a reminder that those who passed beneath the giant statues  were under the governance of the Pharaoh and subject to his majesty.

In 1964, the Egyptian Government completed building a hydroelectric dam above Aswan to provide power and to control the flood cycle of the Nile. This dam would create Lake Nasser and submerge many historic sites.  Abu Simbel was one of those sites.  

UNESCO, created a fund to save the most important of the sites.  As a result, Abu Simbel and the cliff in which it was carved, were carefully cut apart and reassembled like a giant puzzle on a higher site.  

It was one of the greatest engineering feats of historical conservation ever achieved, and a fitting tribute to Ramesses the Great, one of Egypt's most enduring historical figures.

http://i-cias.com/egypt/abu_simbel03.htm shows a picture of the statues being reconstructed at the new site.

A description of the process of the reconstruction is detailed in the article of Dr. Zahi A. Hawass in the Egypt Air Magazine.
http://www.egyptair.com.eg/docs/publicity/story_2_april2001.htm