Complex sentence: St John's Abbey and the house of Sir Charles Lucas were captured despite fierce defence and the Royalist fortifications at St Mary's church were completely destroyed by artillery fire and with it the Royalists' main artillery battery.
Split into simpler sentences: St John's Abbey and the house of Sir Charles Lucas were captured despite fierce defence. The Royalist fortifications at St Mary's church were completely destroyed by artillery fire and with them the Royalists' main artillery battery.