Places such as Poverty Point, Mound City, and Chaco Canyon remind us that the siting of ritual infrastructure in ancient North America was a matter of cosmological precedent. The cosmic gravity of these places gathered persons periodically in numbers that challenged routine production. Ritual economies intensified, but beyond the material demands of hosting people, the siting of these places and the timing of gatherings were cosmic work that preconfigured these outcomes. A first millennium AD civic-ceremonial center on the northern Gulf Coast of Florida illustrates the rationale for holding feasts on the end of a parabolic dune that it shared with an existing mortuary facility. Archaeofauna from large pits at Shell Mound support the inference that feasts were timed to summer solstices. Gatherings were large, judging from the infrastructure in support of feasts and efforts to intensify production through oyster mariculture and the construction of a large tidal fish trap. The 250-year history of summer solstice feasts at Shell Mound reinforces the premise that ritual economies were not simply the amplification of routine production. It also suggests that the ecological potential for intensification was secondary to the cosmic significance of solstice-oriented dunes and their connection to mortuary and world-renewal ceremonialism.