Old Lessons

Kevin Lewis

January 11, 2020

The Growth and Decline of the Western Roman Empire: Quantifying the Dynamics of Army Size, Territory, and Coinage
Sabin Roman & Erika Palmer
Cliodynamics, 2019


We model the Western Roman Empire from 500 BCE to 500 CE, aiming to understand the interdependent dynamics of army size, conquered territory and the production and debasement of coins within the empire. The relationships are represented through feedback relationships and modelled mathematically via a dynamical system, specified as a set of ordinary differential equations. We analyze the stability of a subsystem and determine that it is neutrally stable. Based on this, we find that to prevent decline, the optimal policy was to stop debasement and reduce the army size and territory during the rule of Marcus Aurelius. Given the nature of the stability of the system and the kind of policies necessary to prevent decline, we argue that a high degree of centralized control was necessary, in line with basic tenets of structural-demographic theory.

Ennio Piano & Byron Carson
Rationality and Society, forthcoming


At their arrival in North America, travelers from the Old Continent were exposed to a radically different civilization. Among the many practices that captured their imagination was scalp-taking. During a battle, the Native American warrior would often stop after having killed or subdued the enemy and cut-off his scalp. In this article, we develop an economic theory of this gruesome practice. We argue that scalp-taking constituted an institutional solution to the problem of monitoring warriors' behavior in the battlefield under conditions of high information costs.

Climate Shocks, Political Institutions, and Nomadic Invasions in Early Modern East Asia
Weiwen Yin
Journal of Conflict Resolution, forthcoming


While a large literature argues negative climate shocks can trigger conflicts, recent findings suggest moderate climatic conditions lead to war. This article proposes a conditional theory by incorporating political institution as a moderating variable. I argue that, under the impact of negative climate shocks, centralized societies can mobilize more resources for war, compared to decentralized societies. Thus, the former is more likely to resort to well-organized plundering to address the scarcity problem caused by detrimental climate shocks. Besides, centralized societies have little incentive to plunder when the climatic conditions are moderate, as they can collect taxes regularly through centralized institutions. A comparison between the more centralized Manchurian and the less centralized Mongols on their conflictual behavior serves as an empirical test. I find that temperature was negatively associated with the probability of Manchurian invasion after they embraced centralization but had a positive effect on the likelihood of Mongol invasion.

Playing Vikings: Militarism, Hegemonic Masculinities, and Childhood Enculturation in Viking Age Scandinavia
Ben Raffield
Current Anthropology, December 2019, Pages 813-835


Although the Viking Age (ca. 750-1050 CE) is often characterized as a time of violence, significant questions remain regarding how conflict was conducted during the period. For example, there have been few attempts to understand the cultural norms, attitudes, and practices that drove individuals to participate in warfare. This article reports the results of a study that sought to shed light on this issue by considering the process of enculturation during Viking Age childhood. This was achieved by exploring how the influences of militarism and hegemonic masculinity conditioned those living within Scandinavian societies to participate in conflict from a young age. Through examining the archaeological and literary evidence for childhood pastimes, the study found that everyday aspects of Viking Age society reinforced militaristic, hegemonic hierarchies of masculinity. This can be seen, for example, in the form of toy weapons that were modeled on full-sized, functional weapons; strategic board games that conveyed messages regarding the ideological power of kingship; and physical games that provided opportunities for successful individuals to enhance their social status. The evidence therefore suggests that Viking Age societies perpetuated a series of self-reinforcing cultural norms that encouraged participation in martial activities.

Statistical reliability analysis for a most dangerous occupation: Roman emperor
Joseph Homer Saleh
Palgrave Communications, December 2019


Popular culture associates the lives of Roman emperors with luxury, cruelty, and debauchery, sometimes rightfully so. One missing attribute in this list is, surprisingly, that this mighty office was most dangerous for its holder. Of the 69 rulers of the unified Roman Empire, from Augustus (d. 14 CE) to Theodosius (d. 395 CE), 62% suffered violent death. This has been known for a while, if not quantitatively at least qualitatively. What is not known, however, and has never been examined is the time-to-violent-death of Roman emperors. This work adopts the statistical tools of survival data analysis to an unlikely population, Roman emperors, and it examines a particular event in their rule, not unlike the focus of reliability engineering, but instead of their time-to-failure, their time-to-violent-death. We investigate the temporal signature of this seemingly haphazardous stochastic process that is the violent death of a Roman emperor, and we examine whether there is some structure underlying the randomness in this process or not. Nonparametric and parametric results show that: (i) emperors faced a significantly high risk of violent death in the first year of their rule, which is reminiscent of infant mortality in reliability engineering; (ii) their risk of violent death further increased after 12 years, which is reminiscent of wear-out period in reliability engineering; (iii) their failure rate displayed a bathtub-like curve, similar to that of a host of mechanical engineering items and electronic components. Results also showed that the stochastic process underlying the violent deaths of emperors is remarkably well captured by a (mixture) Weibull distribution. We discuss the interpretation and possible reasons for this uncanny result, and we propose a number of fruitful venues for future work to help better understand the deeper etiology of the spectacle of regicide of Roman emperors.

Cooked starchy rhizomes in Africa 170 thousand years ago
Lyn Wadley et al.
Science, 3 January 2020, Pages 87-91


Plant carbohydrates were undoubtedly consumed in antiquity, yet starchy geophytes were seldom preserved archaeologically. We report evidence for geophyte exploitation by early humans from at least 170,000 years ago. Charred rhizomes from Border Cave, South Africa, were identified to the genus Hypoxis L. by comparing the morphology and anatomy of ancient and modern rhizomes. Hypoxis angustifolia Lam., the likely taxon, proliferates in relatively well-watered areas of sub-Saharan Africa and in Yemen, Arabia. In those areas and possibly farther north during moist periods, Hypoxis rhizomes would have provided reliable and familiar carbohydrate sources for mobile groups.


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