Alexander had now set a determined pace that would bring his army straight into heart of the Persian empire, the city of Persepolis. While one of Alexander's generals lead his troops on a southerly loop through Shirazz, Alexander and 20,000 elite soldiers took a short cut through a narrow path in the Zagros Mountains known as the Persian Gates. Alexander was deep into the pass before he realized he had fallen into a trap. The Persians had built a wall at the narrowest part of the gap and were waiting for him. Stones, javelins, and artillery rained down on the unsuspecting troops. Leaving their dead behind, Alexander's men withdrew. There had to be another way, but Alexander interrogated prisoners to no avail. Finally, a local shepherd came forward. There might be a way, he offered; a narrow and difficult path around the back of the pass. Could an army pass through there, Alexander asked. Absolutely not, the shepherd replied. Alexander ordered his men forward on that very route. Against all odds, Alexander's army crossed the secret and treacherous trail at night and closed his own trap on the Persians. Exactly where was this path? Our local guides debated this well into the night. But, morning found us on the path one of them first thought impossible. Alexander came here in January, he said. The snows would be too deep. Yet this had to be the only way.