Did anyone see this the other day on Slashdot?
http://science.slashdot.org/article....&tid=99&tid=14
Apparently some folks at MIT are recreating a design from Archimedes from before 200 B.C. for a death ray. Actually it's a lens to focus light onto an attacking (wooden) boat with the purpose of setting it on fire. They basically did a proof of concept and it actually IS feasible!
If you follow the other link to MIT, you can see lots of info and pictures. Pretty amazing.