ilization of the Aztecs and Toltecs was developed not in the wonderfully prolific tierra caliente, but on the arid plateaus of Old and New Mexico; persisting while the builders of Palenque and Copan had already passed into oblivion. It seems as though a strange infatuation had possessed these ancient nations in the preference given to bare, sun-scorched plains and mountains, as against the cool shades of the forest-clad countries, which in later times have almost monopolized the abodes of advanced civilization.
It may be said, of course, that forests offer the inconvenience of affording concealment to a lurking enemy; a serious consideration during the ages when a state of war was the normal condition of mankind. Again, it is said that the necessity of clearing away the forest before cultivation was possible offered an obvious inducement toward the utilization, first, of the treeless regions.
The former consideration doubtless weighed strongly in the first beginnings of settlement. And yet our Saxon forefathers, both in the old and new continents, have managed remarkably well in their forested countries, in the face of lurking enemies both animal and human. As regards the difficulty of clearing the forest lands for cultivation, it is amply offset by the necessity, almost universally existing in treeless countries, of providing irrigation if cultivation is to be anything more than a lottery. For forests are limited by a certain minimum of rainfall, below which regularity of crops is dependent upon artificial irrigation.
In other words, the countries which have harbored most of the ancient civilizations are regions of deficient rainfall and compulsory irrigation. And as irrigation means heavy investments of capital or labor, hence the co-operation of many and the construction of permanent works: it necessarily implies the correlative existence of a stable social organization, with protection for property rights, and (in view of the complexity of the problem of proper and equitable distribution of water) a rather advanced appreciation of the need and advantages of co-operative organization.
If, then, the general practice of irrigation is conditioned upon a not inconsiderable degree of advancement in social organization, shall we attribute the development of the ancient civilizations referred to only to its conservative influence, or are there other factors that have contributed toward the preference and long-continued permanence of these polities or populations?
The high cost of irrigation is usually found to be compensated by the high and regular production of the lands irrigated; it is almost a maxim that irrigated lands can support a much denser population than those of countries in which rainfall is relied upon for the production of crops, and where therefore frequent
