Thickness of Ancient shields?

[richsc]

I can buy 100 feet/30 meters of 1.5mm or 2mm edge banding wood strips and be assured it will be that thickness. I am not sure how a Roman carpenter could possibly do that with a manual tool such as a draw knife. It may be possible with a special plane so it might be like a cheese slicer, but modern carpenters assure me that can't work.

I would think the shield tapers to the edge. But, what would be the combat advantage of tapering? Flexibility upon impact?