Explanation My journey began many years ago, after I left University. I traveled thousands of kilometers by all means of transportation available: buses of all kinds, from luxurious models to the most modest ones, airplanes of all sizes, including jets, small craft, planes with propellers and even amphibious ones. I drove my own car, rented others, made long trips on horseback, of course, and, if there was no other choice, I just walked. I slept in all kinds of inns and hostels; to paraphrase Le�n Felipe, 'from comfortable suites to humble rooms'. At times I had to navigate in small boats, ferries and even paddle canoes. Perhaps I was inspired by the early 20th century voyages of the Norwegian explorer-naturalist Carl Lumholtz, or by the earlier travels of Alexander Von Humboldt and those of the famous French poet and surrealist, Anton�n Artaud in the 20th century. Most certainly, I found the inspiration necessary to write up my experiences in the magnificent work of the Frenchman Jan Marie L'Eclezio, El sue�o mexicano. My objective was to visit the ruins of what in ancient times had been the magnificent cities of Mexico and attempt to understand for myself, the grandeur of the conceptions of the architects and urban planners of those times. To enrich my perceptions, I read the chronicles of some writers from the early years of European colonization, who were astonished by what they saw. The Mexican nation brought together a polycultural, multiethnic mosaic of peoples that succeeded in preserving their original culture almost intact despite living, in some cases, in hard to reach geographical areas, far from our grand, modern urban centers and even from those that rose to splendor at that time. In most cases, I was able to verify that despite their flight to what the Mexican anthropologist Gonzalo Aguirre Beltr�n has called "regions of refuge" in their effort to preserve their cultures from the devastating effects of conquest (first Mexica and later Spanish), these peoples did not escape from certain forms of acculturation and syncretism of their pristine customs and ways of life. However, the indigenous element still appears in various ways amidst the everyday life of modern Mexican society. On many occasions it was while I was there among the heirs of those legendary civilizations, sharing with the people, taking measurements, obtaining photographs and layouts of their buildings, eating their dishes and reviewing studies by specialists, that I was able to approach this incredible universe, visible only to those who wish to see it. To begin my narration, then, we turn to descriptions of what a city is...