Double Envelopment is a tactic used by Hannibal Barca.
The double envelopment at Cannae
Example
Used by Hannibal against a massive Roman army of 85,000 at the Battle of Cannae. By forcing the romans to commit so many troops to a forward attack, Hannibal allowed his troops to be pushed back. This caused the Romans to commit more troops to the centre. Hannibal than had is hidden heavy African spearman attack the flanks preventing the romans from manoeuvring. Hannibal's cavalry closed in on the rear to complete the trap. 70,000 romans were killed, about 10,000 were captured and only 6,000 managed to escape. It is considered one of the most impressive military manoeuvres in history.