Dotted around the Citadel, 15 stepped pyramids once topped with flat-roofed temples provide excellent examples of the talud-tablero style, where a vertical structure (tablero) is combined with a sloping wall (talud). The Temple of Quetzalcóatl, built in 150 AD, was rediscovered in 1921 by Manuel Gamio. The façade, which is almost intact despite having lost its bright colours (reproduced in the Museum of Mexico), is a superb example of Teotihuacan architecture.