But afterwards it was proved that Machu Picchu is not Vilcabamba. According to one theory, it was the royal retreat. Other theory states that it was a religious place. Also it is believed that it was an ancient fortress. Because of its location, the city was easily defendable. Think of the steep trail and drawbridges – it was really difficult to conquer the city. But still nobody knows which theory is the true one. That is why it is so mysterious.