What makes Mesoamerica a single field of study is a set of institutions shared across languages and centuries. David Carrasco's survey sets out the principal ones. A 260 day divinatory count and a 365 day solar year run together and mesh into a calendar round of fifty two years, after which the combination repeats; the closing of that cycle was marked in central Mexico by extinguishing every fire and kindling a new one.
The ballgame is played on masonry courts from the Gulf coast to Honduras across two thousand years, and it is not only sport. Courts sit within ceremonial precincts, the game is associated with the passage of the sun and with the underworld, and in the Popol Vuh the Hero Twins are summoned to Xibalba because their play disturbs its lords.
Bloodletting and sacrifice belong to the same economy. The gods are understood to have given their own substance to set the world moving, and human offerings, from the piercing of tongue and ear to the killing of captives, are repayment on a running debt rather than appeasement of anger. The atlas records both the practice and the vocabulary in which it was justified, and notes that the scale reported by Spanish witnesses remains a matter of continuing scholarly argument.