Complex sentence: Despite the difficulties the Byzantine Emperor did not abandon the obstacle and ordered his general Nicephorus Xiphias to take his soldiers and go round the high Belasitsa mountain and surround the Bulgarians, while he himself continued the assaults of the wall.
Split into simpler sentences: Despite the difficulties the Byzantine Emperor did not abandon the attack. Ordering his general Nicephorus Xiphias to manouvre his troops around the high Belasitsa mountain and surround the Bulgarians, while he continued the assaults on the wall.