From the Make Magazine blog:

Because it's been so popular with our viewers, this will be our third attempt at a story called Archimedes Death Ray. The myth is that the [Greek] army defended themselves from invading [Roman] ships by lining the shores with 300 soldiers. But these soldiers did not use conventional warfare. By using their mirrored shields to focus the sun's rays at the invading ships they could, the myth alleges, set the invading ships on fire and save the city.

WHAT WE NEED
300- 350 Volunteers to operate mirrors for the one day of experiment (engineering and science backgrounds preferred)

VOLUNTEERS

* We would require volunteers to be 18 years or older and to Pre-register with us prior to the experiment date by email.
* All volunteers would be required to sign a Participant Release/Liability waiver.
* Experiment will take place in September (date still to be determined).
* Volunteers will need to be available from 9am to 7pm and would have to bring their own lunch and transport themselves to the location (similar to going to an outdoor concert). Possible locations include the Greek Theater, Oyster Point Marina or Alameda NAS.
* We'll supply volunteers with a MythBusters T-shirt, a signed autograph card and possibly a group photo with Jamie and Adam.

HOW TO GET INVOLVED
Send and email to: myths_volunteers@beyond.com.au
Please provide Full Name, Age and Contact Information
Please write [*MythBusters - Death Ray*] in the subject header.
MythBusters will then follow up and contact them with more details very
soon.

We've commented on Mythbusters' earlier attempts ... back in 2005 ... a bit later that year ... and in 2006 ...

... I assume they'll realize that the convex nature of ancient shields doesn't lend itself to focussing the sun's rays ...