The Cambridge History of India, Vol. I: Ancient India v1.c25.8

v1.c25.8

A mountain barrier still separated the Yavana host at Kandahār in the summer of 329 from the Kābul valley, that is to say, from the river system of the Indus. And it would seem that, when the passes filled with the first winter snows, the Yavanas had not yet crossed it. But the army led by Alexander was one which defied ordinary obstacles. In winter¹, under circumstances that made regular provisioning impossible, by extraordinary endurance² it pushed through the hills and descended into the Kābul valley. The princes of the Punjab might feel that the outlandish host stood indeed at the door.