Complex sentence: The Old Mole, stretching into the Bay of Gibraltar, provided further mountings for cannon to sweep the isthmus, while a series of defensive works constructed on a glacis above the entrance to the town provided further enfilading fire.
Split into simpler sentences: The Old Mole, stretching into the Bay of Gibraltar, provided further mountings for cannon to sweep the isthmus. A series of defensive works constructed on a glacis above the entrance to the town provided further enfilading fire.