Here are some links I gathered a while ago when I was looking for
information on them myself:
http://www.aloha.net/~hawmtn/pyramid.htm
http://funny.wox.org:8080/greatstructures/great_main.htm
http://ce.eng.usf.edu/pharos/wonders/pyramid.html
The first one is really good and gives the mathematics involved.
hope this helps
-tgq
