Complex sentence: Some believe the walls were a form of fortification, while others believe it was only used to form the head of the Puma that Sacsayhuamán along with Cuzco form when seen from above.
Split into simpler sentences: Some believe the walls were a form of fortification. Others believe the complex was built as the head of the Puma, the shape which "Sacsayhuamán" together with Cuzco form when seen from above.