They understood this, and prepared to defend the pass. Some Persian troops joined them. They built walls and barricades across the narrow passages. They collected great stones on the brinks of precipices, and on the declivities of the mountains, to roll down upon the heads of their enemies. By these and every other means they attempted to stop Alexander's passage. But he had contrived to send detachments around by circuitous and precipitous paths, which even the mountaineers had deemed impracticable, and thus attack his enemies suddenly and unexpectedly from above their own positions. As usual, his plan succeeded. The mountaineers were driven away, and the conqueror advanced toward the great Persian capital.