that
Huehue-Tlapalan was successfully invaded by Chichimecs, meaning
barbarous aboriginal tribes, who were united under one great leader.
Here is one statement (a little condensed) touching this point: "There
was a terrible struggle, but, after about thirteen years, the Toltecs,
no longer able to resist successfully, were obliged to abandon their
country to escape complete subjugation. Two chiefs guided the march of
the emigrating nation. At length they reached a region near the sea
named 'Tlapalan-Conco,' where they remained several years. But they
finally undertook another migration and reached Mexico, where they built
a town called 'Tollanzinco,' and later the city of Tullan, which became
the seat of their government."

This is substantially what is told of the defeat and migrations of the
Toltecs. The history of Ixtlilxochitl adds doubtful modifications and
particulars not found in the "Codex Chimalpopoca." (See Quatre Lettres,
etc.) This Chichimec invasion of Huehue-Tlapalan is placed at a period
which, in the chronology of the native books, was long previous to the
Christian era, and is mentioned to explain the beginning of the Toltec
movement toward Mexico; but the account of it is obscure.

To find a system of chronology in these old books is not surprising when
we consider that even the Aztecs of Montezuma's time knew enough of
astronomy to have a correct measure of the year. The Aztecs adopted the
methods of astronomy and chronology which were used by their
predecessors. They divided the year into eighteen months of twenty days
each; but, as this gave the year only three hundred and sixty days, five
supplementary days were added to each year, and a sixth day to every
fourth year. The bissextile is known to have been used by the Mayas,
Tzendals, and Quiches, and it was probably common.

We can not reasonably refuse to give some attention to their chronology,
even while doubting its value as a means of fixing dates and measuring
historical periods. Its method was to count by equal periods of years,
as we count by centuries, and their chronology presents a series of
periods which carries back their history to a very remote time in the
past. Brasseur de Bourbourg says: "In the histories written in the
Nahuatl language, the oldest certain date is nine hundred and fifty-five
years before Christ." This, he means, is the oldest date in the history
of the Nahuas or Toltecs which has been accurately determined. The