Incan architecture is the most significant pre-Columbian architecture in South America. The Incas inherited an architectural legacy from Tiwanaku, founded in the 2nd century BCE in present day Bolivia. 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 is a surviving example of Inca architecture. Other significant sites include Sacsayhuaman and Ollantaytambo. The Incas also developed an extensive road system spanning most of the western length of the continent.