construction began in ad 142 at the order of emperor antoninus pius, and took about twelve years to complete. pressure from the caledonians may have led antoninus pius to send the empire's troops farther north. the wall was protected by sixteen forts with a number of small fortlets between them; troop movement was facilitated by a road linking all the sites known as the military way. the soldiers who built the wall commemorated the construction and their struggles with the barbarians in a number of decorative slabs, twenty of which still survive.