There seems to be ample evidence pointing to the existence in Xochicalco, of a very important settlement during the late Classic, roughly corresponding to the configuration of the city as we know it, Some of it, in particular the lack of a Coatepantli, the presence of a ceremonial centre along avenues and the remarkable likeness of the northern Daxt to an acropolis,tend to indicate that the city itseff may be of Classic construction. If the above is correct, and since Xochicalco does not have many features that connect it to Teotihuacan, but rather to the Maya Area, Oaxaca, and the Gulf Coast, its role could very well have been that of a rival, instead of a satellite, of the great Classic site, reducing its zone of effective powerin the south by stopping, or at least slowing, the flow between the Valley of Mexico and a region that corresponds somewhat to the States of Morelos. Guerrero. and the Balsas River Basin, traditional suppliers of cotton, cacao and greenstones in P¡ehispanic Mexico, The effect of Xochicalco's existence, along with that of a powerful Classic Cholula, Tajin, and a nascent Tula, would have been the reduction of Teotihuacan's. domain, from a panmesoamerican power, to the control of roughly, the Valley of Mexico. That would not suffice to keep up an urban center of Teothihuacan's size or needs. As a consequence its power would be drastically rcduced and its decline and final fall would ensue. Since Teotihuacan was the central node of a great Mesoamerican network, its decline would produce a release, at the regional level, of its components, that would then be realigned to cope with the new situation. The effect would be a strenghtenins of regional networks and some shifts within them to different pattern centres that could explain some of the phenomena in the Classic-Postclassic transition. Muchas evidencias apuntan la existencia en Xochicalco de un importante asentamiento durante el Clásico Tardío, que corresponde con la configuración de la ciudad que hoy conocemos. Si los datos son correctos, al parecer Xochicalco fue un rival comercial del Valle de México y controló el intercambio en la ruta comercial con el valle y las regiones de Morelos, Guerrero y la cuenca del río Balsas. La existencia de este sitio junto con otros del Clásico Tardío posiblemente provocaron el decaimiento de Teotihuacan y quizá explique el fenómeno del periodo de transición entre el periodo Clásico y el Postclásico.