As the Inca Empire was predominantly agrarian, the integration of local farming communities into a corporate agricultural system constituted a great challenge for the imperial political economy. The authors thus analyse an unusual circular structure in the Altos de Arica region of northern Chile, which resembles an important building—called ‘sunturhuasi’—in the capital, Cusco. They explore this structure using three-dimensional modelling, identifying its probable use in astronomical observations and hence its clear connection with the Inca agricultural calendar, ultimately suggesting that it was central to an imperial built environment related to the political economy of maize production.