From the MIT site: "Ancient Greek and Roman historians recorded that during the siege of Syracuse in 212 BC, Archimedes (a notably smart person) constructed a burning glass to set the Roman warships, anchored within bow and arrow range, afire."
Archimedes Death Ray is one of those stories that has been hotly debated over the years, with many attempts to recreate it. I first saw MythBuster trying to recreate this story with limited results. Now, MIT is taking their turn trying to recreate it.
IMHO, in the end the results of both experiments proved that in order for this device to work that there would have to be a lot of ideal conditions. For example, the ship would have to stay perfectly still long enough while the death ray focused the sun's energy on it.
Personally, I would think it would be a much better use of this device to try to focus the sun's light to temporarily blind the crews of the ships or the archers.
Watch the video here.