The Maya had a sacred year of 260 days, an official year of 360
days and a solar year of 365 + days. The fact that 18X20 =360
seems to account for the break in the vigesimal system, making 18
(instead of 20) uinals equal to 1 tun. The lowest common multiple
of 260 and 365, or 18980, was taken by the Maya as the "calendar
round," a period of 52 years, which is "the most important period in
Maya chronology."

We may add here that the number systems of Indian tribes in North
America, while disclosing no use of the zero nor of the principle of
local value, are of interest as exhibiting not only quinary, decimal, and
vigesimal systems, but also ternary, quarternary, and octonary sys-
tems. ¹

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