Complex sentence: Within minutes thousands of his warriors die under the onslaught and the Boman attempt to retreat across the bridge but Julian's armored squad, who managed to evade them while staying on the other side of the bridge open fire into the retreating forces.
Split into simpler sentences: Within minutes thousands of his warriors die under the onslaught and the Boman attempt to retreat across the bridge. Unfortunately for them, Julian's armored squad, which managed to evade them while staying on the other side of the bridge, opens fire into the retreating forces.