I approached through the Istanbul gate. For hundreds of years, this city was one of the westernmost prizes of the Ottomans, with a road that ran straight from here to the capital of the empire. The doors still bear the signs of conflict, bullet holes in the tough black steel. “This city has seen 115 wars, and this fortress has been demolished completely more than 40 times,” noted my guide, Dragana. The grounds are green, dotted with statues and walls and towers, the whole place feeling more like a park, everything bright and happy on a sunny afternoon in the late fall, all of it belying the fierce fighting that has taken place here so many times. “And now, we will see the source of it all,” explained Dragana, bringing our small tour group to the crest of a rise. Below us, the confluence of two mighty rivers, the Sava, …