Teotihuacan (48 kilometers from Mexico City), an ancient religious and administrative city, occupies an 18 square kilometer site, which makes it the largest pre-Columbian city in the Americas. Numerous restoration projects have succeeded one another on the site, unfortunately not very well documented. From the available information, and from present evidence in situ, the author reconstructs the complex series of interventions that took place on the architectural and city-planning elements of the site, analyzing the sometimes arbitrary principles that informed them without attempting to discredit or justify the meaning and objectives of these projects.