T HE SACRED CENOTE , a sink hole in the limestone of the Yucatán peninsula in Mexico, pictured above, looks beautiful. But it holds a dark secret. Between about 600 and 900 AD the Mayan inhabitants of the nearby city of Chichén Itzá, believing it to be a gateway to the underworld, filled the pool with sacrificial riches to the gods: gold, jade, incense, pottery—and people. Those victims, judging by their bones, were often young (half being under 18), and, though more often male than female, were well representative of both sexes.

On the assumption that few of those sacrificed were volunteers, their origin has long been a matter of interest to archaeologists. Some suggest they would have come from afar, perhaps being war captives (as was usually the case with sacrificial victims of the later, Aztec civilisation) or tribute of some sort from conquered lands. Others hypothesise that they were plucked from the local population, perhaps being slaves sold for the purpose by their owners. To try to shed some light on the matter, Douglas Price of the University of Wisconsin, Madison, looked at 40 human teeth recovered from different people cast into the Sacred Cenote. He and his colleagues have just published their results in the American Journal of Physical Anthropology.

The researchers’ interest was in the isotopic ratios, in the teeth under investigation, of two chemical elements: oxygen and strontium. Atomic nuclei are made of protons and neutrons, known collectively as nucleons. The number of protons defines the element to which an atom belongs, but the number of neutrons may vary, the variants being known as isotopes. Oxygen atoms, for example, have eight protons, but may have eight or ten neutrons, for a total of 16 or 18 nucleons. Similarly, strontium atoms have 38 protons but may have 48 or 49 neutrons, for totals of 86 and 87 respectively.

Isotopes of an element are chemically identical, but their different weights mean the physical properties of molecules containing them may differ. For instance, because 18O is heavier than 16O, water containing it tends to fall as rain sooner as storms move inland from the sea, so it accumulates preferentially in freshwater sources near coastlines. This means people dwelling near coastlines imbibe more 18O in their water than do those living inland. Similarly, different rocks, because of the details of their formation, contain different mixtures of strontium isotopes, and these are reflected in the soil which forms from those rocks, and thus in the plants (including crops) which emerge from that soil.

The upshot is that as children grow, and their teeth grow in them, the enamel of those teeth is built from materials reflecting local isotopic ratios. These ratios are sufficiently well known for different parts of Mexico and its neighbours as to permit Dr Price to work out where the owners of the teeth grew up.

Unfortunately for those hoping for a clear-cut answer to the question of whether people cast into the Sacred Cenote were the spoils of distant wars or locals who had drawn the shortest of short straws, the answer to the question, “Where did they come from?” is, “Anywhere and everywhere”. Dr Price and his team could discern no pattern whatsoever. Their analysis suggested that half of the 40 were locals, around a quarter had come from somewhat farther afield, and the remainder from places hundreds of kilometres away, in what are now western Honduras and Mexico’s central highlands. Nor was there an association between birthplace and age. Children were neither more nor less likely than adults to have been locals.

A disappointment, then, for those who like their history neat and tidy. How the priests of Chichén Itzá came by victims remains a mystery. All that can be said for sure is that the gods inhabiting the Sacred Cenote were not choosy. Men, women, adults, children, strangers and locals. All seem to have been equally acceptable to sate their lust for blood.■