Tradefire

Definition: To be able to kill the opponent’s ranged units with your own

Defending archers in a city have a range of 2400 because of the wall bonus while attacking archers only have a range of 1800 meaning the defending archers can get fire onto your marching troops before they have a chance to fire back.

Archer's speed is 500 with full tech meaning if both the defending and opposing archers move then a gap of 1000 has been closed on the battlefield. However if only one set of archers move then the defending archers will get free rounds of firing on your troops, while you archers will keep firing on the opposing layers. This means if the enemy has a larger amount of layers in their city than archers, you will not get any fire on the opposing archers.