When did the middle finger become offensive?

[TheMastersNemesis]

5. Historical Meaning Of The Middle Finger

Historically the middle finger was a gesture used in battle. If the combatant was an archer, the enemy would cut off the index finger so the archer could not shoot his bow in the future. Without the index finger and middle finger an archer cannot draw back his bow and hold an arrow in place. In battles before guns, the archer could have a devastating effect firing at least 200 yards over enemy lines. Thousands of arrows falling from the skies could decimate armies before they got into combat range.

Somehow showing the middle finger was shown as an offensive sign at the enemy as a result of this practice. I believe that the gesture originated from battles between the French and English armies.

Over time the gesture obvious has taken on a different meaning.