The Aztecs did not have the wheel, but they had an intensive agriculture and probably some 12,000,000 peasants were expected to grow a surplus of some 20,000 tons of food for the city and its trading network. They had inherited techniques for quarrying and moving large blocks of stone, as manifested in their so-called calendar stone, a basalt disk 3.6 meters in diameter, 72 centimeters thick and weighing 24 metric tons. It was quarried with stone hammers and chisels, with wooden wedges inserted into cleavage planes. (Ref. 8 , 149 )
On the Goodman-Martinez-Thompson correlation dating system used by the National Geographic Society, the Aztecs did not turn on their previous superiors, the Tepehecs, until 1428 and then by 1519 had a tribute empire that covered most of central Mexico and stretched as far as Guatemala. The other dating correlation system is the "Spinden", which makes all Central American dates about 260 years earlier. The problem is not with relative dates in the American scene, which are consistent by the old Mayan calendars, but with relating these to the Christian calendar. A discovery in Vera Cruz in 1972 seems to confirm the former method to be the most accurate. A map will be found under this same section in the next chapter, showing the progression of the Aztec state and its relationship to other Central and South American empires.
The exact population of Mexico before the arrival of the Spaniards is, of course, unknown. Some have given well thought-out estimates as high as 25,000,000. But, as Braudel (Ref. 260 ) has pointed out, the Indian population of this 15th century suffered a demographic weakness because of the absence of substitute animal milk, a feature which necessitated breast feeding for 3 or 4 years, thus reducing the fertility. This was a factor in the failure of rapid revival of the Indian population after the devastating onslaught of the diseases and firearms of the Spaniards. Outside the Aztec area, Yucatan and the Mayan area of Guatemala were politically divided between petty, rival states. Yucatan continued to remain separate from Mexico until the time of the Mexican revolution.
No reader needs to be reminded that Christopher Columbus reached the Caribbean in 1492, claiming territory for his backer, the Spanish monarchy. All may not know, however, that he had previously sailed far down the coast of Africa and to Iceland and beyond in the north Atlantic, in earlier days. He certainly knew of the presence of Greenland and contrary to some reports, there never was any question about the earth being flat among the sailors of that time. The navigation problem originated, at least in part, from the fact that scientists of the day had accepted Marco Polo's location of Japan as being 1,500 miles off the China coast. This, added to Columbus' adoption of a markedly wrong diameter of the earth, resulted in his assurances throughout his western voyages that he had reached the Indies and was very near China and Japan. On each of his western trips, Columbus rode the Canary Current and the prevailing Atlantic trade-winds. (Ref. 260 ) On the first, he required 36 days from the Canary Islands to his Caribbean landfall. It is of interest that Curtis and Kathleen Saville made essentially the same trip in a rowboat in 1981 in 50 days. The return trip to Europe, however, cannot be made without going first north with the Gulf Stream, or with power. (Ref. 150 , 188 )