Tag Archives: Roman Empire

Ancient Infrastructure and Economic Activity


Roman Roads to Prosperity: Persistence and Non-Persistence of Public Goods Provision

Carl-Johan Dalgaard (University of Copenhagen and CEPR), Nicolai Kaarsen (Danish Economic Council), Ola Olsson (University of Gothenburg) and Pablo Selaya (University of Copenhagen)

Abstract: How persistent is public goods provision in a comparative perspective? We explore the link between infrastructure investments made during antiquity and the presence of infrastructure today, as well as the link between early infrastructure and economic activity both in the past and in the present, across the entire area under dominion of the Roman Empire at the zenith of its geographical extension. We find a remarkable pattern of persistence showing that greater Roman road density goes along with (a) greater modern road density, (b) greater settlement formation in 500 CE, and (c) greater economic activity in 2010. Interestingly, however, the degree of persistence in road density and the link between early road density and contemporary economic development is weakened to the point of insignificance in areas where the use of wheeled vehicles was abandoned from the first millennium CE until the late modern period. Taken at face value, our results suggest that infrastructure may be one important channel through which persistence in comparative development comes about.

URL: http://d.repec.org/n?u=RePEc:cpr:ceprdp:12745&r=his

Distributed by NEP-HIS on: 2018-03-26

Revised by: Martin Söderhäll (Uppsala University)


In the paper Roman Roads to Prosperity: Persistence and Non-Persistence of Public Goods Provision the question “How persistent is public goods provision in a comparative perspective?” is examined by estimating the impact of Roman road-density on various proxies for economic activity today (modern roads, night-lights and population density) and in 500 CE (roman settlements). This is done for areas of Europe, the Middle East and Northern Africa covered by Roman roads in 117 CE. The authors argue that the Roman roads “almost presents itself as a natural experiment” since the main purpose of the roads was to simplify military logistics during Roman times. This led to a road network with roads constructed as straight as possible between nodes, especially in newly conquered and undeveloped areas of the Roman Empire.

roman roads_paris

Figure 1: Roman Roads and Night Lights around Paris

The main findings in the paper are that Roman road density in 117 CE has a statistically significant positive effect on all of the above-mentioned dependent variables, suggesting that the spatial distribution of ancient infrastructure still affects the location of economic activity almost 2000 years later. However, the historical density of ancient infrastructure is not enough to explain the density of modern infrastructure as well as economic activity. The authors hypothesize that persistent use and maintenance of said infrastructure is a necessary condition for the link. To examine the hypotheses the authors’ exploit regional variation in the use of wheeled transport during the first millennia CE. This historical natural experiment is made possible since the Middle East and North Africa abandoned wheeled transport during this period, most probably due to the use of camels, which became a more efficient means of transportation in the region some time during the first millennia (Bulliet 1990).


Figure 2: Roman Roads Network in 117 CE

The developments in the Middle East and North Africa during the first millennia CE led to ancient Roman roads being used to much lesser extent than in Europe were wheeled vehicles (drawn by horses or oxen) continued to dominate among land-based means of transportation up until the nineteenth century. Thus, the authors’ claim, “one should expect influence of Roman roads today only where persistence in infrastructure is found.” In other words, the effect of Roman roads on economic activity today should be insignificant within the Middle East and in North Africa while it should have a positive effect within Europe. However, one should also expect that the density of Roman roads had a positive effect on economic activity in all studied regions before the abandonment of the wheel and the subsequent loss of interest in the use and maintenance of Roman roads in the Middle East and in North Africa.


Figure 3: Relationship between Roman Road Density in 177 CE and Modern Road Density

Econometrically, the hypotheses set by the authors are examined by a cross-sectional specification where the parameter of interest is the influence of Roman road density on various measures of economic activity today and in 500 CE, controlling for (primarily) geographic traits of the grid cells where road density are measured as well as country and language fixed-effects. The empirical results are in line with those hypothesized by the authors. The density of Roman roads had a statistically significant positive effect on economic activity in all specifications except the ones where the modern day variables capturing the degree of economic activity “today” is regressed on Roman road density in the Middle East and North Africa, further strengthening the argument that persistence in infrastructure can explain comparative development over a period of 2000 years.


The interpretation and implication of the empirical result is quite straightforward. It is clearly a good idea to keep investing in infrastructure as long as the infrastructure has an economic value, something the authors show was the case in Europe but less so in the Middle East and North Africa where the value of Roman infrastructure dropped. At first sight, one potential remark is the large time gap between the cross sections. How would the interpretation of the results look like if the link between Roman roads and economic activity disappeared in large parts of Europe some time during the period 500-2010 CE? Results from previous research (Bosker et. al. 2013; Bosker & Buringj 2017) ease the worry of this question slightly, since they have shown a relationship between Roman road-hubs and city sizes during the period 800-1800. However, it would have been nice to see some specifications for the years between 500 CE and 2010 CE in this paper as well, possibly using city sizes from DeVries (2013) or Bairoch (1991) as a proxy for economic activity. Especially since the scope differs a bit from that in Bosker et. al. (2013) where the estimation (to my knowledge) is done in a panel setting and in Bosker & Buringj (2017) where only Europe is studied.

Aside from that, I have very little to remark on; I find the argumentation against potential threats to internal validity convincing, and find arguments against external validity quite irrelevant due to the exploratory nature of the paper. In a way, the paper can be summarized as both fun and fascinating.


Bairoch, P. (1991). Cities and Economic Development: From the Dawn of History to the Present. Chicago, IL: University of Chicago Press.

Bosker, M., Buringh, E., & van Zanden, J. L. (2013). “From Baghdad to London: Unraveling Urban Development in Europe, the Middle East, and North Africa, 800–1800.” Review of Economics and Statistics, 95 (4), 1418-1437.

Bosker, M., & Buringh, E. (2017). “City Seeds: Geography and the Origins of the European City System.” Journal of Urban Economics 98, 139-157.

Bulliet, R. W. (1990). The Camel and the Wheel.  New York, NY: Columbia University Press.

De Vries, J. (2013). European Urbanization, 1500-1800. London: Routledge.


Environmental Shocks and their Effects on Imperial Rome’s State Capacity

Droughts of Dismay: Rainfall and Assassinations in Ancient Rome

By Cornelius Christian (Brock University) and Liam Elbourne (St. Francis Xavier University)

Abstract: We find that lower rainfall in north-central Europe (Gaul/Germania) predicts more assassinations of Roman emperors from 27 BC to 476 AD. Due to agricultural pressures on Germanic tribes, low precipitation caused more barbarian raids. These raids, in turn, weakened the Empire’s overall political stability, and reduced the costs of assassinating an emperor. We buttress our empirical analysis with case study evidence.

URL: http://d.repec.org/n?u=RePEc:brk:wpaper:1703&r=his

Circulated by nep-his on 2017/10/08

Review by Fernando Arteaga (George Mason University)



Was Imperial Rome’s political stability disturbed by environmental shocks? If so, what were the transmission channels? These are the two fundamental questions the authors aim to answer. Their thesis is straightforward: As any pre-industrial society, rainfall levels predicted agricultural output in Roman times. A lack of rain affected food availability, especially in the underdeveloped regions where Northern Germanic Tribes resided, making these societies more prone to raid Roman towns across the border. The incursions then created political conflict among the Romans themselves.


The text relies on econometric analyses and a couple of case studies to back up the argument. The main statistical test is simple: they regress Roman political stability on rainfall data. The main variable they use as a proxy of political unrest is the assassination of Roman emperors (as presented by Scarre 1995): the more emperors were killed, the less stability in the Empire. Alternatively, they also employ an index of inflation and new governmental infrastructure investment as a proxy for stability  (larger inflation and less imperial projects imply improved stability).  The rainfall variable comes from Buengten et al. (2011) own estimations on precipitation levels across France and Germany for all the period under study. Figure 1 displays the main data points used in the analysis. The authors find that negative rainfall shocks are both associated with more emperor’s being killed (Figure 2) and with having larger inflation rates and fewer investment projects. A decrease of one standard deviation in precipitation caused an 11.6% standard deviation increase in assassination probability. The regression is empirically valid because there is no possibility of reversal causality; precipitation is not a factor that may be influenced by Roman politics [1].



Figure 1: Roman Gaul/Germania (Yellow). Rainfall Datapoints (Green). Emperor Assassination Locations (Red)




Figure 2: The red line indicates the precipitation level, while the blue is the amount of Roman Emperors assassinated.


But how exactly does lack of rain destabilized Roman society? The paper’s hypothesis relies on the Germanic raid linkage: Germanic tribes attacked Rome when they had a poor harvest of their own, which then created unrest in Roman interior stability.  To test such assertion, they regress Germanic/Gaul incursions on the rainfall levels. The raid data they use comes from Venning (2010), who reviewed the many times the Roman Empire suffered raids through its history. The authors find a negative correlation: a decrease in one standard deviation in rainfall is associated with a 4% standard deviation increase in a number of raids. They corroborate the results by doing some robustness tests: 1) a placebo test, in which they regress non-Germanic raids on precipitation levels, which they find that had insignificant impact (which means that precipitation mattered only in Germanic zones, because they were the only ones that really suffered from a lack of rain); 2) an instrumental variable where the relationship between Roman instability and Germanic incursion is instrumented by rainfall. They find that “a standard deviation increase in the raid dummy [the presence of raiding] causes a 29.3% increase in the probability of assassination.”

To give more weight to their results, they present a brief recapitulation on the reigns of two assassinated Roman emperors: Severus Alexander (208-235) and Gallienus (218-268). The key insight is that both emperors faced important challenges on the Eastern and Northern borders, however only the latter had a relevant impact on Roman internal politics. On the East, the Roman Empire frequently collided with the Sassanid Empire (the other larger state in the area), but notwithstanding the severity of the clashes (at some point they even captured a Roman Emperor, the father of Gallienus) it never caused great civil unrest in Rome. However, on the North, Rome bordered the Germanic tribes (scattered non-organized societies) that did affect Rome’s stability.  The conclusion we get from the narrative is that the Germanic border was important/special precisely because it was very susceptible to environmental shocks, which then led to constant raiding; unlike the Sassanid border, in which the Romans faced a cohesive society that could successfully resist bad crops or confront military bravados on non-environmental factors.



I enjoyed reading the paper very much. It made me re-realize why I find Economic History fascinating: it deals with topics that are interesting in themselves (the politics of the Roman Empire! What is not to like about it?), that remain relevant for today’s problems (we still seek to understand the relationship between nature and political conflict very much), and it treats the issues under study with great care and humility (there is no grand universal theory, but a careful attempt to attain a reliable empirical finding- however small that is).

My main concern with the paper is that the authors never clarify the relationship between Northern Rome’s lack of state capacity and the barbarian incursions. The main narrative maintains that the Germanic raids were the source of Roman political unrest (that is the way I summarized the argument in the preceding section). But at several instances across the paper, the authors hint that Roman political complications in Gaul were themselves a precursory factor that made the Germanic incursions more menacing.

The problem is present in both the econometric analysis and in the case studies. If I understood it correctly (by looking at figure 1), the regressions they asses rely on data that captures rainfall in both Roman Gaul/Germania and non-Roman Germania. The argument is that lack of rain affected Germanic independent tribes more because they were less prepared than the Roman borderline towns. Intuitively, this sounds right. However, the assertion does not imply that alternative transmission channels could not matter too. Yes, Roman towns were better prepared to endure bad harvests than their Germanic neighbors, but that doesn’t imply that bad agricultural output in Roman towns could not be the cause of political instability in them. There may be a relevant omitted variable bias problem in the empirical specification. [2]

The problem seems clearer when we consider the conclusions the authors get from their case studies: in them, they compare the level of relevance local border town problems in Germania/Gaul and in Syria had on larger Roman politics. The Germanics were a constant thorn on Rome, but the Syrians weren’t. Why? The authors explicitly stress that Roman Gaul/Germania had lower state capacity than Roman territories next to Syria, and so it was easier to subdue unrest in Syria than in Gaul. However, if that is so, then we are led to beg the question of what causes what? Is weak state capacity due to raiding, or is raiding due to weak state capacity? The paper’s narrative emphasizes the former linkage (all of the quantitative estimations rely on that sole mechanism too) while, at the same time, it recognizes that the latter mattered too. Unfortunately, it never sets to disentangle the underlying causality. [3]


Buengten, Ulf et al. (2011)  “2,500 years of European climate variability and human
susceptibility.” Science, 331(6017), pp. 578-582

Scarre, Chris (1995) Chronicle of the Roman Emperors: The Reign-by-Reign Record of the Rulers of Imperial Rome. Thames & Hudson: London.

Scheidel, Walter (2015) “Orbis: the Stanford geospatial network model of the Roman world.” http://orbis.stanford.edu/

Venning, Timothy. (2010) A Chronology of the Roman Empire, Bloomsbury Academic: New York.


[1] The authors confirm this by regressing rainfall at time t on lagged t -1 political stability.  It is interesting to note that this obvious observation may not be true for current events. Climate change is indeed affected by the domestic politics of some countries.

[2] I also remain confused about what data was used for some of the alternative estimations. For example, on the placebo test, they regress non-Germanic raids on precipitation levels. I assume they are using non-Germanic precipitation levels too. Otherwise, it would mean they would be testing how rain in Germania affects raids in non-Germania, which would make no sense.  However, they don’t clarify.

[3] My two cents on the Syrian/Gaul distinction is that geography and travel times may explain it. ORBIS (A project that reenacts the geospatial framework of the Roman Empire) allows us to estimate the times and cost of regular trips to different cities in the Roman Empire. A trip from Rome to Cologne would last 32 days on the fastest route and 63 days on the cheapest. A trip from Rome to Palmyra, on the other hand, would last 28 on the fastest route and 42 on the cheapest. This can provide a benchmark of the cost of mobilizing resources across regions: moving a Roman army could be 1/3 cheaper if it had to go to Syria rather than Germania. This significative figure implies that the costs of subduing unrest in Germania were larger and so more difficult.