Tree rings
One ring per year: width and density record growing conditions, season by season.
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The Roman Climate Optimum
About two thousand years ago, the lands around the Mediterranean got some very lucky weather: many warm years with just the right amount of rain. Fields gave lots of wheat, ships carried it everywhere, and the city of Rome could feed a huge number of people. Scientists call this lucky period the Roman Climate Optimum.
Between roughly 100 BCE and 200 CE the Mediterranean experienced unusually warm, wet and stable conditions — the Roman Climate Optimum. Reliable harvests in Egypt and North Africa fed an empire of some sixty million people, and cheap, dependable grain underpinned Rome's politics, army and growth.
The Roman Climate Optimum — the phase of warm, humid and remarkably stable conditions between the late Republic and the Antonine age — is now central to how historians explain the empire's demographic and economic expansion. Agricultural surpluses in Egypt and North Africa sustained the annona system, urbanisation on a premodern peak, and the fiscal machinery that CASAM's research programme studies.
Nature's archives
How do we know what the weather was like so long ago? Nature kept a diary! Trees add one ring every year — fat rings mean good years. Old ice traps tiny bubbles of ancient air. Mud at the bottom of lakes piles up layer by layer. Reading them is like reading nature's secret notebook.
No Roman ever wrote down the temperature — so scientists read proxies: tree rings record growth year by year, Alpine ice cores trap ancient air, lake sediments stack seasonal layers. Together, these natural archives let researchers reconstruct rainfall and temperature with surprising precision.
Palaeoclimatology gives ancient history an instrumental record it never had: dendrochronological series, ice cores and varved lake sediments provide annually resolved proxies for temperature and precipitation. CASAM's programme treats these scientific archives not as background but as sources in their own right — to be criticised, calibrated and integrated with texts and archaeology.
Three natural archives
Ice cores
Ancient air and impurities trapped in glacier ice, layer after layer.
Lake sediments
Seasonal deposits pile up like the pages of a yearly diary.
The arc of CASAM research
From the Bronze Age to the Early Middle Ages
Select a period to explore
c. 3000–1200 BCE
Palaces, archives, first fiscal states
Palatial economies of the eastern Mediterranean develop the first large-scale record-keeping and redistribution systems. Long-distance exchange binds the Aegean, Anatolia, the Levant and Egypt into a single connective world — the deep background of Mediterranean state power.
c. 1200–500 BCE
Collapse, reinvention, connectivity
After the Late Bronze Age collapse, Phoenician and Greek networks re-knit the sea. Colonisation, alphabetic writing and the first coinages transform exchange — laying the institutional foundations that CASAM research traces across the longue durée.
c. 500–31 BCE
Cities, empires, fiscal experiment
City-states and the Hellenistic kingdoms become laboratories of fiscal policy, monetisation and civic institutions. The fiscal regimes of the Hellenistic states are a core research focus of CASAM's community.
31 BCE–284 CE
Integration and the Roman Climate Optimum
The Mediterranean becomes one political and economic space. Demographic growth, labor organization, urban systems and agrarian production reach a premodern peak — under climatic conditions historians now read through natural archives.
284–800 CE
Climate, plague, and transformation
Climatic shifts, pandemics and political transformation remake the ancient world. CASAM studies these ruptures as tests of societal resilience — integrating paleoclimate, archaeogenetic and textual evidence.
Check your understanding
Five quick questions — instant feedback, no grades, just learning.
1. What was the Roman Climate Optimum?
It was a climatic phase, roughly from the late 1st century BCE to the 2nd century CE.
2. Where does our evidence for ancient climate mainly come from?
Nature recorded what no ancient author ever measured.
3. Which of these is NOT a natural climate archive?
Coins tell us about economy and politics — not about rainfall.
4. What happened from the 3rd century CE onwards?
Growing climatic instability coincided with political and epidemic crises — how the two are linked is a major research question.
5. How do historians use climate data today?
Integration — treating scientific archives as historical sources — is exactly CASAM's approach.
Your score:
Sources & further reading
- Kyle Harper, The Fate of Rome: Climate, Disease, and the End of an Empire, Princeton University Press, 2017.
- Michael McCormick et al., “Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence”, Journal of Interdisciplinary History 43/2, 2012.
- Research on climate, disease and society by the CASAM community, including the work of Prof. Sabine R. Huebner (University of Basel).
For teachers
A printable kit with discussion prompts and classroom activities is in preparation.