Since this is the off topic forum I wonder if anyone can verify the following ledgend:

During the Hundred Years war the French cut off the middle fingers of the English archers so that they couldn't put their bows back anymore. So when the English and the French lined up in their battle formations the English archers would give the French "the middle finger" to show that they were capable of killing the French. This is where the "middle finger" gesture came from.

This is an interesting opinion on the matter that I found from looking at wikipedia:
http://www.straightdope.com/classics/a980904.html