Hi
This is a basic tactic for newbies to get easy wins against the computer.
It needs 3 infantry units and effective against 2 infantry + 1 archer or 1 infantry + 2 archer as well.
1. You have to move your infantry behind an obstacle but dont compress your armies in a pile because a pile cant flank effectively just a right order of units one above another.
2. When the enemy is close enough send the upper unit into southwest, then the middle unit into southwest too but a bit closer, finally attack the front enemy with the lower unit.
3. When the two front clash your middle unit will be above, attack them from north and send the third unit into south. Dont bother with the archers, it is better if you eliminate the infantry quickly and then you can finish the archers easily.
4. Attack the enemy from left with your third unit. If your army looks like an U and the enemy looks like an O the victory is close.
5. If you perform the flank well the first enemy will flee soon and you can beat the second enemy with your overpower.
6. When the hostile infantry flee the archer unit become easy target.
In 1 infantry + 2 archer line-up it is just easier. If you have 6 units can make this in both sides of the obstacle.