There was a short window that their army needed to cover both quickly and quietly.
It was a gap between the cover offered by the rolling hills and the future forests in the distance. The only thing keeping them from being seen was a particularly well-placed hill in the lands below. It protected them from the most direct angle of sight offered to the moving enemy masses. But, it didn't protect them entirely. It would only have taken one scout unit to round the hill in a different direction to the main forces, and they would have been caught.
Yet, somehow, that did not happen.
