caernarfon03 Arrowloops Arrow loops are a familiar defensive feature of medieval fortifications, allowing the maximum field of fire through the minimal external opening. At Caernarfon, they reached the peak of deadly ingenuity. Here the embrasures are contrived to allow up to three crossbowman to discharge their bolts through a single external loop (slit). thus enabling a fast and deadly crossfire to be laid down - in effect a kind of medieval machine-gun. The arrangement demanded considerable skill and discipline from the bowman, who formed the mainstay of the castle's defense.