Inca architecture is the most significant pre-Columbian architecture in South America. The Incas inherited an architectural legacy from Tiwanaku, founded in the 2nd century B.C.E. in present-day Bolivia. A core characteristic of the architectural style was to use the topography and existing materials of the land as part of the design. The capital of the Inca empire, Cuzco, still contains many fine examples of Inca architecture, although many walls of Inca masonry have been incorporated into Spanish Colonial structures. The famous royal estate of Machu Picchu (Machu Pikchu) is a surviving example of Inca architecture. Other significant sites include Sacsayhuamán and Ollantaytambo. The Incas also developed an extensive road system spanning most of the western length of the continent and placed their distinctive architecture along the way, thereby visually asserting their imperial rule along the frontier.