A Shiite king ruled northern Syria more than a millennium ago from behind the towering walls of the citadel in Aleppo. In later centuries, Arab armies repelled medieval crusaders from the hilltop fortress, Mongol invaders damaged it and Ottomans used it as military barracks.

By 2011, the citadel had settled into what seemed a comfortable retirement as a UNESCO world heritage site and tourist attraction, illuminated at night by artistic ground lights and surrounded by the bustling cafes of Aleppo's old city below.

But today, in the third year of a bloody civil war that has killed more than 70,000 Syrians, the hulking fortress has resumed its strategic role of earlier eras. President Bashar Assad's forces have taken up positions in it to shell their enemies, and Syrian opposition fighters say they are desperate to capture it.