The chronological system of the Mexicans, by which they determined the date of any particular event, was also very remarkable. The epoch from which they reckoned corresponded with the year 1091 of the Christian era. It was the period of the reform of their calendar, soon after their migration from Aztlan. They threw the years, as already noticed, into great cycles, of fifty-two each, which they called “sheafs,” or “bundles,” and represented by a quantity of reeds bound together by a string. As often as this hieroglyphic occurs in their maps, it shows the number of half-centuries. To enable them to specify any particular year, they divided the great cycle into four smaller cycles, or indictions, of thirteen years each. They then adopted two periodical series of signs, one consisting of their numerical dots, up to thirteen, the other, of four hieroglyphics of the years.[188] These latter they repeated in regular succession, setting against each one a number of the corresponding series of dots, continued also in regular succession up to thirteen. The same system was pursued through the four indictions, which thus, it will be observed, began always with a different hieroglyphic of the year from the preceding; and in this way each of the hieroglyphics was made to combine successively with each of the numerical signs, but never twice with the same; since four, and thirteen, the factors of fifty-two,--the number of years in the cycle,--must admit of just as many combinations as are equal to their product. Thus every year had its appropriate symbol, by which it was at once recognized. And this symbol, preceded by the proper number of “bundles” indicating the half-centuries, showed the precise time which had elapsed since the national epoch of 1091.[189] The ingenious contrivance of a periodical series, in place of the cumbrous system of hieroglyphical notation, is not peculiar to the Aztecs, and is to be found among various nations on the Asiatic continent,--the same in principle, though varying materially in arrangement.[190]