Complex sentence: The vanguard, with which Queen Eleanor marched, was commanded by her Aquitainian vassal, Geoffrey de Rancon; this, being unencumbered by baggage, managed to reach the summit of Cadmos, where de Rancon had been ordered to make camp for the night.
Split into simpler sentences: The vanguard, with which Queen Eleanor marched, was commanded by her Aquitainian vassal, Geoffrey de Rancon. Unencumbered by baggage, they reached the summit of Cadmos, where de Rancon had been ordered to make camp for the night.