Complex sentence: Today's 5.5 kilometre (3.5 mile) long wall that links these two small communities is in the shape of a pentagon was completed in the 15th century, along with its 40 towers and 5 fortresses.
Split into simpler sentences: Today's 5.5 kilometre (3.5 mile) long wall that links these two small communities has the shape of a pentagon. It was completed in the 15th century along with other 40 towers and 5 fortresses.