A few defiles pass through this barrier to the other side of the north Greek watershed.
This was accomplished without much difficulty, but the main body was still in the defiles in rear, when about 3 p.m.
To cut Alexander's communications with the rear, Darius now committed the error of entangling his large force in the mountain defiles.
Shortly after crossing the Bohemian-Saxon frontier, and whilst still struggling through the sandstone defiles, the stream assumes a north-westerly direction, which on the whole it preserves right away to the North Sea.
But all routes are difficult, winding between granite and limestone rocks, and abounding in narrow defiles and rugged torrent beds.