Exploring the Mystery of the Rise and Fall of Ancient Maya Cities: Drought, Conflict, and Massive Infrastructure - A Model of the Rise and Decline of Ancient Maya Cities

Introduction—"Why Gather in Cities and Why Leave Them"

Cities have always both attracted and let go of people. Recent research has quantified the rise and fall of Classic Maya cities (approximately AD 250–900) as a simultaneous progression of multiple factors rather than a single cause. The key elements are "climate," "conflict," "economies of scale (effects of large-scale infrastructure)," and the difference between the benefits and burdens of urban life. Phys.org

Key Points of the Research—Integrating "Multiple Factors" with a Population Ecology Model

The paper published in PNAS integrates archaeological data on population, conflict, and agricultural infrastructure accumulated since 2012 with high-resolution climate reconstructions and advances in computational modeling. Using the concept of population ecology, it describes "aggregation" into cities and "dispersal" into rural areas. The results explain that the expansion of cities was driven by the shock of aridification and the increase in intergroup conflicts, with the incentive being the joint development of agricultural infrastructure such as irrigation, ridges, and terraces, which provided economies of scale. Phys.org

Interestingly, urban exodus progressed not during "climate deterioration" but rather during improvement phases. The environment around cities deteriorated due to long-term intensive agriculture, and while the marginal costs of cities increased, the improved climate enhanced the **livability of rural areas (recovery of autonomy)**, leading to "de-urbanization" when benefits became less than burdens—a paradoxical conclusion. Phys.org

A Perspective of "Optimization Movement" Rather Than "Collapse"

This research is valuable in that it encompasses the previously separate discussions of the environmental stress theory, war and security theory, and economic factors theory within a single dynamic framework. The "birth, expansion, and contraction of cities" can be explained by the interaction of exogenous shocks (aridification, conflict frequency) and endogenous processes (infrastructure development→ economies of scale→ reinforcement of disparity and patron-client relationships→ environmental degradation around cities). In other words, it replaces the dramatic narrative of "collapse" with optimization behavior. Phys.org

Methods and Data Support

・Data Integration: Integration of archaeological data on population changes, conflict indicators, and agricultural infrastructure investment (accumulated since 2012) with the latest high-resolution climate reconstructions.
・Modeling: Using a concise model of population ecology to explain population movement through changes in the relative expected utility (benefits−burdens) of cities and rural areas.
・Source: Weston C. McCool et al., "Modeling the rise and demise of Classic Maya cities: Climate, conflict, and economies of scale" (PNAS, 2025). Phys.org

These results align with previous studies indicating that aridification can amplify conflicts (e.g., Kennett et al.'s climate-conflict link), but the new work explicitly demonstrates **"de-urbanization during improvement phases"** as a novel point. Nature

Concrete Image—"Economies of Scale" as a Double-Edged Sword

In ancient Maya cities, agricultural infrastructure such as irrigation, ridges, reservoirs, and canals boosted community-scale productivity, justifying aggregation. On the other hand, its sustained intensive use led to ecosystem degradation around cities, eventually causing a decline in marginal efficiency. When environmental conditions in rural areas improved, the "attractiveness of cities" relatively declined. This endogenous cost increase, combined with improving climate, prompted population dispersal, as depicted in this study. Phys.org

Reactions on Social Media—"Discomfort with the Term 'Collapse'" and "Implications for Modern Cities"

After the research was published, PNAS's official social media introduced and spread the study. The summary **"Joint irrigation and defense projects nurtured cities"** was shared, attracting interest not only from the archaeology and history clusters but also from urban policy and climate fields. Facebook

Discussion Point 1: Terminology
In Reddit's history communities, the perspective that "the Maya did not disappear" has been repeatedly expressed, and there has been a shared discomfort with the term "collapse". Many voices perceive this study as supporting that discomfort with the term "de-urbanization." Reddit

Discussion Point 2: Implications for the Present
In urban planning and climate communities, the simplicity of the theorem "cities only persist as long as benefits outweigh burdens" has become a topic of discussion. The paradox that improved external conditions can actually promote "the freedom to leave" has been compared to post-drought rural return and correction of megacity sprawl. Futurity, which handles research news, also introduced the study emphasizing the overlap of multiple factors. Futurity

Discussion Point 3: Significance of Quantification
While there is high appreciation for the point of integrating "environmental stress," "war," and "economics" into a single model, there is also cautious discussion about how well it can absorb local differences (e.g., individual histories of Calakmul, Tikal, Caracol) and the interpretation of parameters. There are calm voices suggesting that expert reviews and related field studies (updates on agricultural productivity and population estimates) should be read together. ScienceDirect

Learning Beyond "Myth"—A Checklist for Modern Cities

1. Types of Shocks: Not only deterioration (drought, security) but also improvement can trigger population movement.

2. Lifespan of Infrastructure: Economies of scale diminish. Can maintenance costs and externalities (environmental impact) be reflected in pricing?

3. Value of Autonomy: Evaluate the "convenience" of cities and the "freedom" of rural areas on the same scale.

4. Multi-Factor Design: Handle climate, security, economy, and social inequality in simultaneous optimization.

Papers and Official Releases

• Paper: Weston C. McCool et al., "Modeling the rise and demise of Classic Maya cities: Climate, conflict, and economies of scale" PNAS (Vol. 122, Issue 42, 2025). Table of contents and summary. PNAS

• Explanation (UCSB The Current): Background and summary of the research. The Current

• General Article (Phys.org): Key points and citations of the research. Phys.org