The general course of Mayan history is indicated unmistakably by four principal lines of evidence capable of being correlated with each other. These are:—
1. Stratigraphic sequences in pottery, stylistic sequences in sculpture, structural sequences in architecture, etc.
2. Traditional history preserved in the Books of Chilam Balam and representing a knowledge of past events at the time of the Spanish Conquest.
3. Dates inscribed on a great number of monuments in terms of the ancient Mayan time counts.
4. Astronomical checks on these inscribed dates.
The artistic position of a monument may be used to validate the contemporaneous character of an inscribed date, otherwise interpretable as referring to the past or future, or it may serve to fix a repeating date in a single historical setting. The events in the traditional history of the Books of Chilam Balam, meager enough when taken alone, have the valuable quality of reaching back into the time of the First Empire when the use of dates on temples and monuments was much in vogue. They permit a richly documented past to be tied in, as it were, to a poorly documented terminal period.
Fig. 36. The Front Head of the Two-Headed Dragon on Stelæ at Piedras Negras showing the Increase in Flamboyant Treatment. The interval between (a) and (b) is 125 years, that between (b) and (c) is 45 years.
Before the matter of the ancient inscribed dates can be understood, however, the somewhat complicated mechanism of the Mayan calendar must be explained, as well as the system of hieroglyphs and the notation of numbers. Then there is the problem of correlation which necessitates delicate adjudications of evidence. Finally we must take up the proofs which demonstrate the astronomical achievements of the Mayas which, in reverse, provide checks upon the correctness of the day for day correlation itself. We must proceed slowly and carefully, without much following of by-ways, however attractive they may appear. We will begin with stratigraphy and stylistic sequence.