Complex sentence: Over 200 cannon and gun ports were set within the walls, and the fort was essentially a firing platform, with a shape that allowed many lines of fire; its low curved bastions were designed to deflect cannon balls.
Split into simpler sentences: Over 200 cannon and gun ports were set within the walls, and the fort formed a firing platform with a shape that allowed many lines of fire. In addition, its low curved bastions were designed to deflect cannon balls.