The sixteen Monasteries on the Slopes of Popocatepetl, built in the 16th century by Augustinians, Franciscans and Dominicans, were designated as a World Heritage Site by UNESCO in 1994 in recognition of their value as a model for the early monasteries and churches of New Spain and beyond. These monasteries have a very large atrium in front of a single nave church with a capilla abierta or open chapel, where mass was held outdoors instead of within the church. The twelve monasteries in Morelos are commonly known as the "Route of the Volcano" or the "Route of the Monasteries" for tourists. In 2021, the Heritage Site was expanded to include the Tlaxcala City Cathedral. The sixteen monasteries are open to visitors, located in Northern Morelos, Puebla and Tlaxcala.