Complex sentence: The volley's and particularly the cauldrons of Greek fire reigned upon the crusaders and the cauldrons of Greek fire were flung straight into the three massive crusader Siege towers, which suddenly went up in flames.
Split into simpler sentences: The volley's and particularly the cauldrons of Greek fire reigned upon the crusaders. The cauldrons of Greek fire were flung straight into the three massive crusader Siege towers, which suddenly went up in flames.