Arrowslits are slits in the walls of a castle and the city walls
where archers fire arrows on the enemies below. Sometimes
the future of the city is in the archers hands because if they
didn't have the archers enemies would take over the city.
A tall thin window like thing but it is just a hole, out of which arrows are
shot; later ones had a slot on its side in the middle to give a wider angle of
fire for crossbows.
we got this picture from www.wikapedia.com