Journal of Interdisciplinary History, LIV:1 (Été, 2023), 1–42.

Seth Bernard, Joseph McConnell, Federico Di Rita,
Fabrizio Michelangeli, Donatella Magri, Laura Sadori,
Alessia Masi, Giovanni Zanchetta, Monica Bini,
Alessandra Celant, Angela Trentacoste, Lisa Lodwick,
J.. Troy Samuels, Marta Mariotti Lippi, Cristina Bellini,
Claudia Paparella, Dan-el Padilla Peralta, James Tan,
Peter van Dommelen, Andrea U. De Giorgi, and Caroline Cheung
An Environmental and Climate History of the
Roman Expansion in Italy In 400 B.C.E., Rome was the
largest of the Latin-speaking cities of western central Italy. Political
power was monopolized by a group of religiously privileged land-

Seth Bernard is Associate Professor, University of Toronto. He is author of Historical Culture in
Iron Age Italy: Histoire, Archaeology, and the Use of the Past, 900–300 BCE (Oxford, forthcoming).
Joseph McConnell is Research Professor, Desert Research Institute. He is co-author of
“Lead Pollution Recorded in Greenland Ice Indicates European Emissions Tracked Plagues,
Wars, and Imperial Expansion during Antiquity,” Proceedings of the National Academy of Science,
CXV (2018), available at doi.org/10.1073/pnas.1721818115.

Federico Di Rita is Assistant Professor, Dept. of Environmental Biology, Sapienza Uni-
versity of Rome. He is co-author of “Holocene Forest Dynamics in Central and Western
Mediterranean: Periodicity, Spatio-Temporal Patterns and Climate Inﬂuence,” Nature: Scien-
tiﬁc Reports, VIII (2018), available at doi.org/10.1038/s41598-018-27056-2.

Fabrizio Michelangeli is Research Fellow, Dept. of Environmental Biology, Sapienza
University of Rome. He is co-author of “Three Millennia of Vegetation, Land-Use and Cli-
mate Change in SE Sicily,” Forests, XIII (2022), available at doi.org/10.3390/f13010102.

Donatella Magri is Professor, Dept. of Environmental Biology, Sapienza University of
Rome. She is co-author of “Sign-Switching Ecological Changes in the Mediterranean Basin
à 4.2 ka BP,” Global and Planetary Change, CCVIII (2022), 103713, available at https://doi.org
/10.1016/j.gloplacha.2021.103713.

Laura Sadori is Professor, Dept. of Environmental Biology, Sapienza University of
Rome. She is co-author of “Palaeoecological Data Indicates Land-Use Changes across Europe
Linked to Spatial Heterogeneity in Mortality during the Black Death Pandemic,” Nature Ecol-
ogy & Evolution, VI (2022), 297–306.

Alessia Masi is Research Associate, Max Planck Institute of Geoanthropology. She is co-
author of “Timber Exploitation during the 5th–3rd Millennia BCE at Arslantepe (Malatya,
Turkey): Environmental Constraints and Cultural Choices,” Archaeological and Anthropological
les sciences, X (2018), 465–483.

Giovanni Zanchetta is Professor, University of Pisa, and Editor at Quaternary Science Reviews.
He is co-author of “Tracking Westerly Wind Directions over Europe since the Middle Holo-
cene,” Nature Communications, XIII (2022), available at doi.org/10.1038/s41467-022-34952-9.

Monica Bini is Associate Professor, University of Pisa. She is co-author of “The 4.2kaBP
Event in the Mediterranean Region: An Overview,” Climate of the Past, XV (2019), 555–577.

© 2023 by the Massachusetts Institute of Technology and The Journal of Interdisciplinary
Histoire, Inc. Published under a Creative Commons Attribution 4.0 International (CC PAR
4.0) license., https://doi.org/10.1162/jinh_a_01971

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SETH BERNA RD E T AL.

owning families known as patricians, but legal reforms in the fourth
century B.C.E. created a more open patricio-plebeian elite (or nobi-
litas), whose membership drew from a wider pool of landowning
families. En même temps, Rome’s legions extended their control
over Latium and then progressively across the peninsula in a process
of state creation and intensiﬁcation of state-directed warfare.

Alessandra Celant is University Researcher, Laboratory of Palaeobotany and Palynology,
Dept. of Environmental Biology, Sapienza University. She is co-author of “Archaeobotanical
and Chemical Investigations on Wine Amphorae from San Felice Circeo (Italy) Shed Light on
Grape Beverages at the Roman Time,” PloS One, XVII (2022), e0267129, available at https://
doi.org/10.1371/journal.pone.0267129.

Angela Trentacoste is Humboldt Fellow, Christian-Albrecht University of Kiel, et
Associated Researcher, University of Oxford. She is co-author of “Heading for the Hills?
A Multi-isotope Study of Sheep Management in First-Millennium BC Italy,” Journal of Archae-
ological Science: Reports, XXIX (2020), available at doi.org/10.1016/j.jasrep.2019.102036.

Lisa Lodwick, who died in late 2022, was University Lecturer in Environmental Archaeol-
ogy, University of Cambridge and Post-doctoral Research Fellow, All Souls College, University
of Oxford. She was author of “Sowing the Seeds of Future Research: Data Sharing, Citation and
Reuse in Archaeobotany,” Open Quaternary, V (2019), available at doi.org/10.5334/oq.62.

J.. Troy Samuels is Instructor in History, Phillips Exeter Academy. He is co-author of
“An Iron Age Settlement at Gabii: An Interim Report of the Gabii Project Excavations in
Area D, 2012–2015,” Etruscan and Italic Studies, LXX (2019), 1–33.

Marta Mariotti Lippi is Associate Professor, University of Florence. She is co-author of
“Ancient Oral Microbiomes Support Gradual Neolithic Dietary Shifts towards Agriculture,»
Communications naturelles, XIII (2022), available at doi.org/10.1038/s41467-022-34416-0.

Cristina Bellini is an Independent Researcher. She is co-author of “Modern Pollen Anal-
ysis in the Estuary Habitats along the Coast of Dhofar (Sultanate of Oman),” Sustainability,
XIV (2022), available at doi.org/10.3390/su141711038.

Claudia Paparella is a Ph.D. étudiant, Dept. of Classics, University of Toronto.
Dan-el Padilla Peralta is Associate Professor of Classics, Princeton University. He is author of

Divine Institutions: Religions and Community in the Middle Roman Republic (Princeton, 2020).

James Tan is Senior Lecturer, Dept. of Classics and Ancient History, The University of

Sydney. He is author of Power and Public Finance at Rome, 264–49 BCE (Oxford, 2017).

Peter van Dommelen is Joukowsky Family Professor of Archaeology, Professor of
Anthropology, and Director of the Joukowsky Institute for Archaeology and the Ancient
Monde, Brown University. He is co-editor, with Bernard Knapp, of The Cambridge Prehistory
of the Bronze and Iron Age Mediterranean (Cambridge, 2015).

Andrea U. De Giorgi is Professor of Classical Studies, Florida State University. He is

author of Ancient Antioch: From the Seleucid Era to the Islamic Conquest (Cambridge, 2016).

Caroline Cheung is Assistant Professor of Classics, Princeton University. She is author of

Dolia: The Containers that Made Rome an Empire of Wine (Princeton, forthcoming).

This paper publishes results from a conference held at the University of Toronto, spon-
sored by the Departments of Classics and of Art History, and the Archaeology Centre, et
supported by a Social Science and Humanities Research Council Connection Grant from the
Government of Canada. The authors wish to thank Giuseppe Castellano and Giacomo
Fontana for logistical support during the conference, and Kyle Harper and the anonymous
reader for helpful feedback.

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C L I M A T E H I S T O R Y OF TH E RO M A N E X P A NS IO N | 3

Through this expansion, the Romans encountered a varied
ecological landscape occupied by heterarchical communities with
diverse political and cultural structures. Urban societies of Magna
Graecia and Etruria occupied coastal plains or river valleys that
offered access to arable land and maritime trade routes. The less
urbanized Sabines and Samnites lived in the upland areas of the
Apennines, while societies along the east coast participated in
the cultural and economic circuits of the Adriatic world. By the
mid-second century B.C.E., Rome had conquered all the way to
the Alps, defeating Ligurians, Gauls, and other groups closely
linked to the Iron Age cultures of Transalpine Europe. Although
Rome’s approach to each area variously included extensions of cit-
izenship, colonization programs, or seizures of territory as state
property (ager publicus), Rome showed little interest in controlling
domestic affairs in local communities. Archaeology shows consid-
erable continuity between pre-Roman and Roman cultures in
many places into the ﬁrst century B.C.E.1

Although its parameters remain debated, progressive demo-
graphic growth characterized the period. During the early expan-
sion, settlements in the Italian countryside grew denser (a process
known as rural inﬁlling), and extensive urbanization commenced
autour 300 B.C.E. The increase in urban population was most evi-
dent in the city of Rome itself, which relied on improved access to
grain from Sicily, Sardinia, and North Africa to feed a population
approaching 1 million residents by the later ﬁrst century B.C.E.
Although Rome was a late adopter of coinage, by the second
century B.C.E. a uniﬁed monetary zone had spread across Italy.
Slavery became entrenched at the core of the productive econ-
omy, and trade around Italy and the Mediterranean increased.

1 For an introduction to the historical narrative, see Alan Astin et al. (éd.), The Cambridge
Ancient History (Cambridge, 1990), VIII; Nicola Terrenato, The Early Roman Expansion into
Italy: Elite Negotiation and Family Agendas (Cambridge, 2019); Marian Helm, Kampf um Mitte-
litalien Roms ungerader Weg zur Großmacht (Stuttgart, 2021); for pre-Roman Italy, see Stéphane
Bourdin, Les peuples de l’Italie préromaine (Paris, 2012); for archaeological evidence relating to
territoire, see Elio Lo Cascio and Alfredina Storchi Marino (éd.), Modalità insediative e strutture
agrarie nell’Italia meridionale in età romana (Bari, 2001); for imperialism in northern Italy, see Lo
Cascio and Marco Maiuro (éd.), Popolazione e risorse nell’Italia del nord dalla romanizzazione ai
Longobardi (Bari, 2017); for colonization, Tesse Stek and Jeremia Pelgrom (éd.), Roman Repub-
lican Colonization: New Perspectives from Archaeology and Ancient History (Leiden, 2014); pour
Roman organizations of landholding, see Saskia Roselaar, Public Land in the Roman Republic:
A Social and Economic History of Ager Publicus in Italy, 396–89 BC (Oxford, 2011).

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The cumulative effect of these trends was the eventual integration
of Italy along sociocultural, économique, and political lines. By the
time Augustus established the principate in 29 B.C.E., the diverse
societies of Iron Age Italy appeared transformed into what ancient
sources referred to as “United Italy” (tota Italia).2

The character of early Roman imperialism is long debated,
but scholarship has recently challenged ideas of Roman exception-
alism and any exclusively Roman ideology conditioning initial
imperial success in the fourth and third centuries B.C.E. In that
period, competition between Rome and Italian rivals took place
amid geopolitical transformations that were sweeping over much
of the central Mediterranean. This contextualization of Roman
expansion within broader trends shifts scholarly focus away from
Rome’s intrinsic characteristics to more general and extrinsic
forces such as ecology and climate.3

A desire to bring scientiﬁc data to bear on the history of
Roman expansion is not new. Dans 1962, Ward-Perkins made pio-
neering use of pollen records from Lago di Bracciano to test ancient
accounts of Rome’s armies encountering the supposedly pristine
Ciminian forest of South Etruria. More than half a century later,
evidence from lakes in the region and more effective dating
methods offer better possibilities for reconstruction. Improvements
in the scientiﬁc data are detectable even over the last several years.
These advances are not speciﬁc to the region and period but belong
to wider trends in historical climate studies. Recent reﬁnements of
scientiﬁc methods along with greater attention to collecting histor-
ical and archaeological data allows for the reconstruction of past
climate and landscape beyond and between those punctuated

2 For urbanization, Jamie Sewell, “Higher-Order Settlements in Early Hellenistic Italy: UN
Quantitative Analysis of a New Archaeological Database,” American Journal of Archaeology,
CXX (2016), 603–630; for demography, see Luuk de Ligt, Peasants, Citizens and Soldiers: Stud-
ies in the Demographic History of Roman Italy 225 BC–AD 100 (Cambridge, 2012); Saskia Hin, Le
Demography of Roman Italy (Cambridge, 2013); for economic changes including monetization,
see Nathan Rosenstein, Rome at War: Farms, Families, and Death in the Roman Republic (Chapel
Hill, 2004); Tan, Power and Public Finance at Rome, 264–49 BC (Oxford, 2017); Tymon de Haas
and Gijs Tol (éd.), The Economic Integration of Roman Italy: Rural Communities in a Globalizing
Monde (Leiden, 2017); Roselaar, Italy’s Economic Revolution: Integration and Economy in Repub-
lican Italy (Oxford, 2019).
3 For debate on Roman imperialism, see Craige Champion, Roman Imperialism: Readings and
Sources (Oxford, 2004); Arthur Eckstein, Mediterranean Anarchy, Interstate War, and the Rise of
Rome (Berkeley, 2006); Terrenato, The Early Roman Expansion into Italy; Padilla Peralta, “Epis-
temicide: The Roman Case,” Classica, XXXIII (2020), 151–186.

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C L I M A T E H I S T O R Y OF TH E RO M A N E X P A NS IO N | 5
moments of abrupt change or catastrophe that ﬁrst attracted atten-
tion. The ﬁeld consequently moves toward more subtle and dia-
chronic histories of human-environment relationships.4

Thus far, cependant, this shift has had less impact on the study
of Roman climate, which remains dominated by a focus on later
imperial history and the role of climate in the empire’s disintegra-
tion. In this debate, there starts to appear an implication that the
earlier period’s climate was more stable and, by extension, plus
conducive to state formation. Although this view has not been
expressed in explicit terms, it often emerges implicitly with refer-
ences to the end of the empire coinciding with the end of a cli-
mate period referred to by climatologists as the “Roman Warm
Period” (RWP, also known as the “Roman Climate Optimum”).
The RWP has thus come to be understood as an ingredient in
Rome’s early imperial success. À ce jour, scholarship on the RWP’s
parameters and its historical implications has been inconsistent in
both scientiﬁc and historical literature. There is no consensus on
the timing of the RWP’s onset, with suggested dates ranging from
550 à 200 B.C.E. and even as late as 1 B.C.E. There has also been
little explicit consideration of exactly how the RWP supported
Roman imperialism. We might imagine, Par exemple, a view that

John-Bryan Ward-Perkins, “Etruscan Towns, Roman Roads and Medieval Villages: Le
4
Historical Geography of Southern Etruria,” Geographical Journal, CXXVIII (1962), 389–404;
for broader applications of scientiﬁc data to historical climate studies, see Dagomar Degroot
et coll., “Towards a Rigorous Understanding of Societal Responses to Climate Change,»
Nature, DXCI (2021), 539–550; see also Sverker Sörlin and Melissa Lane, “Historicizing Cli-
mate Change—Engaging New Approaches to Climate and History,” Climatic Change, CLI
(2018), 1–13; for the Anthropocene and historical climate studies, see Deepak Chakrabarty,
“The Climate of History: Four Theses,” Critical Inquiry, XXXV (2008), 197–222; Adam
Izdebski et al., “Realising Consilience: How Better Communication between Archaeologists,
Historians and Geoscientists Can Transform the Study of Past Climate Change in the
Mediterranean,” Quaternary Science Reviews, CXXXVI (2016), 5–22; Catherine Kearns, “Med-
iterranean Archaeology and Environmental Histories in the Spotlight of the Anthropocene,»
History Compass, XV (2017); John Moreland, “AD 536—Back to nature?” Acta Archeologica,
LXXXIX (2018), 91–111; for Roman antiquity showing focus on later periods, see Michael
McCormick et al., “Climate Change during and after the Roman Empire: Reconstructing the
Past from Scientiﬁc and Historical Evidence,” Journal of Interdisciplinary History, XLIII (2012),
169–220; Kyle Harper, The Fate of Rome: Climat, Disease and the End of an Empire (Princeton,
2017); Harper and McCormick, “Reconstructing the Roman Climate,” in Walter Scheidel
(éd.), The Science of Roman History: Biology, Climat, and the Future of the Roman Past (Princeton,
2018), 11–52; Izdebski and Michael Mulryan (éd.), Environment and Society in the Long Late
Antiquity (Leiden, 2019); Paul Erdkamp, Joseph Manning, and Koenraad Verboven (éd.),
Climate Change and Ancient Societies in Europe and the Near East: Diversity in Collapse and Resil-
ience (New York, 2021).

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SETH BERNA RD E T AL.

climate was stable enough to fade into the background, granting
room for social development, or that the RWP played a more active
role by increasing marginal returns on agricultural labor, by allow-
ing for more extensive cultivation, or by facilitating demographic
expansion or more reliable maritime trade; these and other histor-
ical models remain untested.5

Although global indices may reﬂect a period of an overall
warmer climate commencing around 300–200 B.C.E., local data
suggest considerable differences of the timing and expression of this
trend across Italy, something that makes sense in light of the pen-
insula’s fragmented ecologies. This variability suggests that the idea
of a uniﬁed RWP is overly simplistic, while human responses to
environmental and climatic change were themselves highly com-
plex. We do not dispute the role of climate and environment in
Italian state-formation and economic development but focus atten-
tion on the human agency and the societal resilience that charac-
terized human-environmental relationships during the Roman
expansion in Italy. Drawing upon an array of archaeological, scien-
tiﬁc, and historical approaches, we propose that the history of Italy’s
climate and environment during this period is best studied through
the practices by which communities and households mitigated risk.
Such inquiry makes clear that Rome intervened in ongoing Ital-
ian practices of landscape management, that climate became most
historically salient in relation to (or when mediated by) Italian
societies’ resilience practices, and that such strategies made Italian
communities robust in an unpredictable environment.

5 For a collection of dates suggested for the RWP’s onset, see Harper, The Fate of Rome, 321 n. 46.
Hubert Lamb, Climat, History and the Modern World (Londres, 1995), 142; see also McCormick
et coll., “Climate Change during and after the Roman Empire,» 203; Harper and McCormick,
“Reconstructing the Roman Climate”; Tan, “Climate Change and Rome’s Changing Repub-
lique,” in Mattia Balbo and Federico Santangelo (éd.), A Community in Transition: Roman History,
200–134 BC (Oxford, 2022), 21–54; Giulia Margaritelli et al., “Persistent Warm Mediterranean
Surface Waters during the Roman Period,” Scientiﬁc Reports, X (2020). For scientiﬁc critique
of the RWP in Italy, see Bini et al., “Hydrological Changes during the Roman Climatic Optimum
in Northern Tuscany (Central Italy) as Evidenced by Speleothem Records and Archaeological
Données,” Journal of Quaternary Science, XXXV (2020), 791–802; for hydrological variability during
the Roman period, see John Haldon et al., “Plagues, Changement climatique, and the End of an Empire:
A Response to Kyle Harper’s The Fate of Rome (1): Climat,” History Compass, (2018) XVI,
available at doi.org/10.1111/hic3.12508; Elena Xoplaki et al., “Hydrological Changes in Late
Antiquity: Spatio-Temporal Characteristics and Socio-Economic Impacts in the Eastern Medi-
terranean,” in Erdkamp, Manning, Verboven, Climate Change and Ancient Societies, 533–560.

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C L I M A T E H I S T O R Y OF TH E RO M A N E X P A NS IO N | 7

NATURAL ARCHIVES FOR CLIMATE A synthesis of the current
understanding of the environment and climate of central Italy
and neighboring regions conﬁrms relatively few short-term
extreme climate shifts during the period of Roman expansion.
During the ﬁrst millennium B.C.E., the central Mediterranean
saw global and macroregional climate ﬂuctuations related to
changes in solar magnetic activity and the North Atlantic Oscilla-
tion (NAO, a prominent and recurrent pattern of variability in
atmospheric circulation over the North Atlantic). The strength
of two hemispherical pressure patterns—a low near Iceland and
high over the Azores and the subtropical region—reﬂects the
NAO’s positive or negative mode. In a negative mode, these fea-
tures are weak, tracking storms directly across the western Medi-
terranean and bringing comparatively more precipitation to Italy
and the surrounding region. The NAO thus represents a dominant
source of atmospheric variability affecting the climate of the west-
ern and central Mediterranean on a multi-decadal scale. Recon-
struction of the NAO index from a combination of lake cores, arbre
rings, and speleothems showed a mainly negative NAO phase inter-
rupted by a positive phase around 750–500 B.C.E. Around 500 B.C.E.,
the NAO shifted back to negative and then returned to a prolonged
positive phase about 150 years later.6

Negative phases of NAO correlated with minima in solar
energy; reconstruction of Total Solar Irradiance (TSI) showed
two solar minima in the ﬁrst millennium B.C.E. The ﬁrst

6 Eduardo Zorita et al., “The Global Climate System,” in Sam White, Christian Pﬁster,
Franz Mauelshagen (éd.), The Palgrave Handbook of Climate History (New York, 2018), 21–
26; for NAO, see James W. Hurrell et al., An Overview of the North Atlantic Oscillation (2003);
Harper and McCormick, “Reconstructing the Roman Climate,» 15; Celia Martin-Puertas
et coll., “Regional Atmospheric Circulation Shifts Induced by a Grand Solar Minimum,” Nature
Geoscience, V (2012), 397–401. Leslie J. Gray et al., “Solar Inﬂuences on Climate,” Reviews of
Geophysics, XLVIII (2010), available at doi:10.1029/2009RG000282. Jesper Olsen et al., “Vari-
ability of the North Atlantic Oscillation over the Past 5,200 Years,” Nature Geoscience, V
(2012), 808–812; Ilya Usoskin et al., “Grand Minima and Maxima of Solar Activity: Nouveau
Observational Constraints,” Astronomy & Astrophysics, CDLXXI (2007), 301–309; Gerard
Bond et al., “Persistent Solar Inﬂuence on North Atlantic Climate during the Holocene,»
Science CCXCIV (2001), 2130–2136; Johan C. Faust et al., “Norwegian Fjord Sediments
Reveal NAO Related Winter Temperature and Precipitation Changes of the Past 2800 Years,»
Earth and Planetary Science Letters, CDXXXV (2016), 84–93; for the tendency of NAO to express
differently across the Mediterranean, see Brian J. Dermody et al., “A Seesaw in Mediterranean
Precipitation during the Roman Period Linked to Millennial-Scale Changes in the North
Atlantic,” Climate of the Past, VIII (2012), 637–651.

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8 |

SETH BERNA RD E T AL.

figue. 1 Global Climate-Forcing Trends Affecting Italy in the First

Millennium B.C.E.

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Johan C. Faust et al., “Norwegian Fjord Sediments Reveal NAO Related Winter
SOURCES
Temperature and Precipitation Changes of the Past 2800 Years,” Earth and Planetary Science
Letters, 435 (2016), 84–93; Friedrich Steinhilber et al., “Total Solar Irradiance during the
Holocene,” Geophysical Research Letters, 36 (2009).

(c. 800–600 B.C.E.) is often referred to as the Halstatt or Homeric
grand solar minimum. A second minimum with almost identically
low levels of TSI but of shorter duration occurred around 375–
250 B.C.E. (see Fig. 1). A period of comparatively high solar energy
followed from the later third century B.C.E. The link between the
NAO and TSI suggests that periods of solar minima are relatively
cooler and wetter in the western and central Mediterranean.7

7 Bond et al., “Persistent Solar Inﬂuence”; Friedrich Steinhilber et al., “Total Solar Irradi-
ance during the Holocene,” Geophysical Research Letters, 36 (2009); Luis E. UN. Vieira et al.,
“Evolution of Solar Irradiance during the Holocene,” Astronomy & Astrophysics, DXXXI
(2011).

C L I M A T E H I S T O R Y OF TH E RO M A N E X P A NS IO N | 9

Recent research emphasizes explosive volcanism as the largest
driver of short-term global climate variability. This happens when
sulfur dioxide gas, a major constituent in volcanic emissions, est
transformed in the atmosphere to highly reﬂective sulfate aerosols
that shield the earth from solar radiation, resulting in cooler air
temperatures. When the volcanic plume of large eruptions reaches
the stratosphere, sulfate aerosols remaining in the atmosphere for
months to years can lead to pronounced, long-term cooling at
global scales. Because they are highly soluble, sulfate aerosols from
smaller eruptions where the volcanic plume only extends into the
troposphere are quickly removed by precipitation, leading to
relatively small, localized cooling. Ancient sources noted local
eruptions of smaller volcanoes like Etna or Vesuvius during our
period, but such activity was not signiﬁcant enough to drive global
effects.8

Linking climate drivers such as volcanic eruptions ﬁrst to
changes in precipitation and temperature and second to historical
events requires exact and independent dating of all records,
especially if inferring causality between them. Volcanic sulfur
fallout measured in polar and alpine ice cores provides detailed
records of thousands of years of explosive volcanism. The mag-
nitude, seasonal timing, and location—the latitude in particular—
of the erupting volcano largely determined impacts to the
climate.

Technological improvements for ice core analyses have led to
a rapid increase in the number of high-resolution volcanic fallout
records for Roman antiquity. Ice cores from Greenland and Ant-
arctica suggest that explosive volcanism during the ﬁnal three cen-
turies B.C.E. was somewhat low relative to the last 2,500 années, à
least until early 43 B.C.E. These records indicate that none of the
twenty-ﬁve largest eruptions of the past 2,500 années, and only
three of the forty largest eruptions, occurred between 300 et

8 Michael Sigl et al., “Timing and Climate Forcing of Volcanic Eruptions for the Past 2,500
Years,” Nature, DXXIII (2015), 543–549; Gill Plunkett et al., “No Evidence for Tephra in
Greenland from the Historic Eruption of Vesuvius in 79 C.E.: Implications for Geochronology
and Paleoclimatology,” Climate of the Past, XVIII (2022), 45–65; for textual attestations of
eruptions in the region, see Richard B. Stothers and Michael R. Rampino, “Volcanic Erup-
tions in the Mediterranean before A.D. 630 from Written and Archaeological Sources," Revue
of Geophysical Research, LXXXVIII (1983), 6358–6360.

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10 | S E T H B E R N A R D E T AL .

44 B.C.E. Two larger eruptions occurred in 430 et 426 B.C.E., et
others clustered between 168 et 158 B.C.E.9

These records indicate one of the largest eruptions of the past
2,500 years early in 43 B.C.E., which was followed by elevated
atmospheric sulfate for nearly three years. Geochemical ﬁnger-
printing of volcanic tephra preserved in the ice shows that the
source was a massive eruption of the Okmok volcano in Alaska.
Atmospheric modelling (Community Earth System Model, CESM,
version 1.2.2) of the event suggested pronounced cooling in 43/2
B.C.E. throughout the Northern Hemisphere, with annual average
temperatures as much as 5°C cooler. These model results were
consistent with global evidence from tree rings and speleothems,
which suggested that 43 et 42 B.C.E. were among the coldest of
the last 2,500 années. The CESM simulations indicated substantial cli-
mate effects in the area of Roman activity, including average sum-
mer and fall temperatures that were 4.5°C colder in 43 B.C.E. et
2°C colder in winter and spring in 42 B.C.E. Although precipitation
is notoriously difﬁcult to simulate, results suggested that 43 B.C.E.
summer precipitation was 50 à 120% above normal in southern
Europe, with autumn precipitation up to 400% above normal in
some regions. Josephus and Appian recorded extreme weather,
famine, and epidemic disease from early 43 to late 42 B.C.E.10

Jihong Cole-Dai et al., “Comprehensive Record of Volcanic Eruptions in the Holocene
9
(11,000 Years) from the WAIS Divide, Antarctica Ice Core,” Journal of Geophysical Research:
Atmospheres, CXXVI (2021); Sigl et al., “Timing and Climate Forcing of Volcanic Eruptions”;
Anders Svensson et al., “Bipolar Volcanic Synchronization of Abrupt Climate Change in
Greenland and Antarctic Ice Cores during the Last Glacial Period,” Climate of the Past, XVI
(2020), 1565–1580; McConnell et al., “Pervasive Arctic Lead Pollution Suggests Substantial
Growth in Medieval Silver Production Modulated by Plague, Climat, and Conﬂict,»
Proceedings of the National Academy of Sciences of the United States of America, CXVI (2018),
14910–14915. Uncertainties in the most up-to-date ice chronologies are probably <1 year for antiquity. Sigl et al., “Timing and Climate Forcing of Volcanic Eruptions”; for impact of volcanic activity in the Ptolemaic Empire, see Manning, al. “Volcanic Suppression of Nile Summer Flooding Triggers Revolt Constrains Interstate Conﬂict Ancient Egypt,” Nature Communications, VIII (2017); Ram Singh, “Investigating Hydroclimatic Impacts of the 168–158 B.C.E. Quartet Their Relevance to Nile River Basin and Egyptian History,” Past, XIX (2023), 249–275. 10 Josephus, Antiquities Jews, Book XIV 12.310; Appian, The Civil Wars, IV, 122, V, 25; McConnell “Extreme after Massive Eruption Alaska’s Okmok Volcano 43 BC Its Effects on Wars Late Roman Republic,” Proceedings of National Academy Sciences United States America (2020); CESM, Hurrell et “The Community Earth System Model: A Framework Collaborative Research,” Bulletin American Meteorological Society, XCIV (2013), 1339–1360; sources, P. Y. Forsyth, “In Wake Etna, 44 B.C.,” Classical Antiquity, VII (1988), 49–57. l D o w n o a d e d f r o m h t t p : >
Journal of Interdisciplinary History, LIV:1 (Été, 2023), 1–42. image

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