This paper proposes a cross-civilizational hypothesis: the hexadecimal (base-16) measurement system is not the product of abstract mathematical design, but rather the historical sediment of geometric constraints imposed by rice paddy irrigation. As the only wetland crop domesticated by humans, wet rice cultivation requires precise water-level management, and the physical necessity of both intake and drainage channels naturally produces a perpendicular cross structure, dividing cultivated land into four-unit cells. This geometric constraint received its earliest written record in the Chinese oracle bone character "田" (field) — a square bisected by a cross, representing the bird's-eye view of a paddy irrigation system. Through demand-driven elaboration (taxation, trade), the quaternary structure self-replicated into 4×4=16, producing hexadecimal measurement units. Cross-civilizational comparison — China (16 liang = 1 jin, attested in the Han Shu), India (Harappan weights in 1:2:4:8:16 series), Vietnam (16 luong = 1 can), Thailand (1 rai = 4 ngan, explicitly suited to paddy delineation) — validates the hypothesis: wherever large-scale wet rice agriculture existed, quaternary or hexadecimal traces appear in measurement systems. Babylon (dryland agriculture → base-60) and the Maya (maize → base-20) provide inverse controls. This paper does not claim that rice cultivation is the sole pathway to hexadecimal; rather, we argue that the rice-irrigation geometric hypothesis offers the most parsimonious single explanation for the cross-civilizational evidence, and we propose a testable prediction: the depth and antiquity of wet rice civilization correlates positively with the systematization of hexadecimal measurement.
Chen et al. (Mon,) studied this question.