Cool. I found out from thewebtoday that Xerxes reputedly built a canal in Greece and now there may be some evidence of it.

That sent me off to Google. There I found some pictures (the latter with the appropriate selection from Herodotus (so here's another map relative to Herodotus' history) and a tourist map (the canal was apparently dug near Nea Roda (thinnest part of the more eastern peninsula)). If you haven't got the idea yet, or need to brush up on your history, here's a summary of the The Persian Wars. Finally, just to be complete, and give Google its due, here's another history with a less-detailed map.

(I'm going to post this on MetaFilter, too, so if you're curious, you can check it for comments.)