Climate change, DNA, and the Roman Empire

Review of The Science of Roman History: Biology, Climate and the Future of the Past, ed. Walter Scheidel, Princeton University Press, Princeton & Oxford 2018

Contents

Introduction                                                                                                            1
Walter Scheidel

Chapter 1. Reconstructing the Roman Climate  11
Kyle Harper & Michael McCormick

Chapter 2.  Archeobotany: The Archeology of Human- Plant Interactions  53
Marijke van der Veen

Chapter 3. Zooarcheology: Reconstructing the Natural and Cultural Worlds from Archeological Faunal Remains  95
Michael MacKinnon

Chapter 4. Bones, Teeth, and History  123
Alessandra Sperduti, Luca Bondioli, Oliver E. Craig, Tracy Prowse, & Peter Garnsey

Chapter 5. Human Growth and Stature  174
Rebecca Gowland & Lauren Walther

Chapter 6. Ancient DNA  205
Noreen Tuross & Michael G. Campana

Chapter 7. Modern DNA and the Ancient Mediterranean   224
Roy J. King & Peter A. Underhill

Review for classicists                                          © James Jope 

(This review is followed by M. Eleanor Irwin's paper on the olive as an index of climate change.)

Perhaps the two most familiar achievements applying recent scientific methods in classical studies are the use of tools like infrared light to render damaged papyrus legible to reveal new ancient texts, and the climatological explanation of strange reports of a cold, sunless summer leading to crop failures in late antiquity.

The anthology reviewed here surveys scientific methods which may revolutionize classical history in the future. The cover design juxtaposes an Ionic column with the helical structure of DNA

(deoxyribonucleic acid, or genes). The keynote chapter concerns climate change, with others on paleobotany, new techniques to analyze bones and teeth, and DNA. The papyrological advances are not included, although the introduction alludes to them. Their absence reflects the character of this anthology. Most of the contributors are scientists and/or archeologists who are distinguished in their own fields but apparently have little first-hand knowledge of the classical corpus (Scheidel and Garnsey are notable exceptions), and many of the examples discussed relate to prehistoric times or regions outside the Roman Empire. There are also ‘how to’ instructions for applying the methods, which will mainly interest archeologists. But the purpose of the book is to foster awareness of the future importance of these sciences for Roman history. As the authors too concede, this will not be only a bilateral project between archeology and the sciences, it will require multidisciplinary collaboration involving traditional studies of written sources as well. In some cases, however, it will be the responsibility of this reviewer, and of the reader, to indicate the relevance of classical scholarship. The editor, in his introduction, points to the role of traditional scholarship: “while the temporal association between trends in macro-social development and climatic conditions is increasingly well documented, the complexity of causal relations remains very much in need of detailed analysis …we must ask not only how Roman society was affected by environmental forces but also how it responded”. Yet his greater enthusiasm for science is betrayed when, after enumerating what science can tell from bones—the sex, age, diet, diseases, and cause of death of an individual—he exclaims, “Never before has it been possible to examine individual Roman lives in such detail.” So much for ancient biographers!

Chapter 1: climate change

In 536 CE written sources reported a year without summer, with cold temperatures and veiled sunlight. We now know that this was caused by a series of volcanic eruptions. The airborne ashes which blocked the sunlight also dropped sulfate deposits. The nascent science of paleoclimatology has recovered these deposits from chronologically graded ice cores in Greenland to trace the eruptions. Ice cores, tree rings, glacial advances and recessions, sedimentary layers in lakes and caves all provide ‘proxy’ evidence of past climate changes. Even variations of solar activity (sun spots) can be traced by the radionuclide isotopes which they leave in ice cores and tree rings.

Proxy findings are used to build overall climate patterns for the present geological epoch (Holocene). They show a period of comparatively stable warmth and moisture in the Mediterranean from approximately 200 BCE to 150 CE, known as the Roman Warm Period or Roman Climate Optimum, which favored the growth of the empire. Also local variations are attested: Egypt, for example, was affected more by the climate factors of the Indian Ocean than was the Mediterranean, so that its reliability as the imperial granary diminished after 156 CE.

Links with specific historical events are still speculative. The Huns who pushed the Goths into the empire may have been prodded by a drought in Central Asia. The science is young and there are many gaps, and comparative studies of archeological and written evidence will have to connect the dots. The authors do not seem to have much confidence in new insights from classical sources: They compare the “large and growing” archeological and paleoclimatological evidence with a “nearly static set of written records” (39).

Chapter 2: archeobotany

New methods have also influenced archeobotany. Isotopes (variants of biologically active elements like oxygen, nitrogen, or carbon), DNA, and scanning electron microsopy (more powerful than visible microscopy) are used to investigate carbonized, waterlogged, desiccated or mineralized plant remains. Exotic arable weeds attest to long-distance trade, and recovered plant species indicate a general improvement and variation of diet in the Roman period in both Egypt and Britain-- and not only for the elite. Pears, plums, cherries, walnuts, cabbage, leaf beets, even apples were introduced into Britain by the Romans.

Although the only mention of ancient agricultural writings here is a warning to read them “in their temporal, cultural, and regional contexts, rather than as reliable guides to agriculture across the entire Greco-Roman world” (60), the author reports that the philosophy of paleobotanists has shifted from a deterministic view in which plant and soil properties shape human developments to a more sociocultural view in which both plants and people have agency. Thus, the potencies of spice plants coupled with the demand for luxury promoted long-distance trade. With this philosophy, the door is wide open for fresh investigations of ancient texts.

Chapter 3: faunal remains

This chapter suggests “new directions” for zooarcheology, although some of them simply extend methods used previously on human remains. Isotopes, dental wear, and DNA differentiate goats and sheep and their varieties, as well as their diet, which could reveal new evidence on, e.g., the extent of transhumance (seasonal moving of livestock to different pastures) in the classical world.

The author warns against archeologists becoming too obsessed with scientific techniques, which he calls ‘processual’. ‘Postprocessual’ work includes scholarship. Some archeologists’ distaste for ‘theory’, he argues, is wrong because their own practice implies theoretical presuppositions. Questions of ethnic groups, social classes, etc. cannot be answered by scientific techniques. (114)

Chapters 4-5: bones and teeth, growth and stature

This section details anthropological methods working especially with bones and teeth, but it again sounds a note of caution by calling attention to conflicts and errors within anthropology related to these methods. Radiology, microscopy, isotopes, measurements and computerized multivariate statistical analyses can reveal sex, age at death, diseases, diet, etc. However, the ‘markers’ on bone used to trace certain diseases can be left by more than one disease. The criteria used to determine age at death, and stature have not been standardized. Thus, historians have inferred high stature for Romans—implying good health and diet-- based on findings which are disputed among anthropologists themselves. Growth estimates can be improved by focusing on infants; stature estimates by preferring full skeletal measurements over calculations from measurements of long bones. Nevertheless, the future of this science should go beyond identifying features of individuals and reconstruct general population traits.

Again in Chapter 4, the authors call for balancing scientific and traditional methods. For example, because oxygen isotopes depend on local weather, they can signal migration. But to investigate why people migrated, historical and literary evidence must be consulted.

Chapters 6-7: DNA ancient and modern

Starting from modern DNA, mutations (genetic changes) can be traced and mapped with ‘molecular clocks’ to reconstruct human phylogenies (lines of descent). Ancient DNA is usually damaged and fragmented, but can still identify pathogens and human subgroups.

Tracing phylogeny is complicated by the circumstance that in every generation, the genetic materials from the two parents undergo ‘recombination’; i.e., they are paired in a way which produces a unique set of individual traits. Two types of DNA do not recombine: Mitochondrial DNA, which is located apart from the ‘chromosomes’ carrying the genes (and actually originated from external organisms which were incorporated by the cells of our ancestor species), is passed down only through the maternal line. And the Y (male sex) chromosome is inherited paternally. Chapter 7 uses Y chromosomes to construct a phylogeny of mankind which is consistent, e.g., with what we know about Neanderthals.

Both types of DNA can be processed more cheaply and quickly now that the initial method used in the 1990s (polymerase chain reaction) has been succeeded by ‘whole-genome sequencing’. Hence we can expect this science to expand.

Specific findings noted by the authors are interesting in relation to possibilities of philological study which remain unnoticed by the authors. Comparison of modern Tuscan and ancient Etruscan genes shows that they are not related, and that the Etruscans were more closely related to Near Eastern peoples. The authors call for further genetic research, but do not mention the obvious path of correlating this finding with the Near Eastern affinities suggested by linguists. Horses grew in size during the Empire, but the genetic evidence does not resolve whether this was achieved through breeding, nurture, or imports; the authors call for more sequencing, but do not discuss any breeding data from ancient agricultural texts. If there are none, the argument ex silentio would still be relevant.

Some classicists may find this book a difficult read. The explanatory prose can be opaque, as in

“leveraging the hierarchy of time-calibrated nested modern haplogroups and glimpses of ancient uniparental and autosomal DNA” (238) 

or

“This predisposition with respect to the lack of random mating creates subdivision such that metapopulations comprised of various subpopulations often get established” (226)  

…where ‘metapopulations’ is not defined. Neither are ‘eukaryote’, ‘allele’ and occasional other terms. Nevertheless, I recommend this book because its content may be critical for twenty-first century scholarship.

I have posted below, with the author’s permission, an exemplary illustration of what a classicist can contribute. This paper by M. Eleanor Irwin was prepared for the 2018 annual meeting of the Classical Association of Canada. The full text appears here for the first time. Notice how it discusses the Roman writers “in their temporal, cultural, and regional contexts, rather than as reliable guides to agriculture across the entire Greco-Roman world” and “not only how Roman society was affected by environmental forces but also how it responded”.

The olive as an indicator of climate change in the Roman agricultural writers

M. Eleanor Irwin

© M. Eleanor Irwin
submitted to the 2018 annual meeting of the Classical Association of Canada

Introduction: the Roman Warm period

We are very much aware of climate change and its effect on us but we may not realize that there were periods of climate change in the past, one of which has a potential interest for Classicists. It is generally agreed by climate scientists that between about 100 BCE and 200 CE there was a period of relatively higher temperatures, first named “the Roman Warm Period” in a 1995 University of Michigan dissertation by W.P. Patterson, also known as the Roman Optimum Period. Climatologists have raised the possibility of a causal connection between this stable climate, the rise of the Roman empire and in particular the period of peace and stability in the 2nd century CE. In this paper I will be looking for awareness of climate change in the agricultural writing of Varro, Vergil, Pliny and Columella during the Roman Warm period and comparing what Cato wrote before and Palladius after this period.
A good place for a Classicist to begin is with Neumann’s 1985 article which surveys climate change in the Mediterranean from the Bronze Age and assembles supporting evidence in Classical authors (mostly Greek) for changes in temperature and rainfall levels. For a survey of climate change in the Roman empire from 100 BCE to 600 CE I recommend the 2012 article by McCormick et al. “Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence.” This article is a good introduction to the ways climatologists measure climate variations:

Greenland ice cores, fluctuations in solar radiation, speleothems [stalactites and stalagmites] from Austria and Turkey, tree-ring series from central Europe and Asia, Austrian and other Alpine glacier movements, varve records [sediment layers] from European and western Asian lakes, and written and archeological records.

Roman agricultural writers

The Romans were interested in farming and recording methods of getting the best results. I will be drawing material from six Roman agriculture writers: Cato the Elder De agricultura, Varro Res Rusticae, Vergil Georgics, Columella Res rustica, Pliny the Elder Naturalis Historia and Palladius Opus agriculturae. Cato lived (234 – 149 BCE) before the beginning of the warm period. Varro, Vergil, Pliny and Columella were active during the Roman Warm Period: Varro (116-27 BCE) and Vergil (70-19 BCE) in the last century BCE and Pliny (23-79 CE) and Columella (an older contemporary of Pliny’s, White 1970, 36). Palladius lived much later, probably in the fourth century CE. All were land owners and all but Pliny had considerable first-hand experience in farming. In addition to these works which survive, there were many others now lost, of which I will mention two: Saserna, the name of a father and son writing after Cato and before Varro, used as a source by Varro and Columella (White 1970, 20), and the Carthaginian Mago whose work in Punic was translated into Greek and Latin after the destruction of Carthage in 146 BCE (White 1970, 17-8).

Mediterranean climate and the olive

Much of Italy, especially the west coast between the sea and the Apennine mountains, has a Mediterranean climate with hot dry summers and mild wet winters.  Other areas in the Mediterranean with this climate are the southern part of Spain, the coast of France bordering the Mediterranean, Greece, the Aegean and Mediterranean coast of Turkey, the coast of Syria, Lebanon and Israel and in Africa the coast of Morocco, Algeria, Tunisia and a small part of Libya. Crops grown in a Mediterranean climate include such fruit as grapes, figs and pomegranates and, most characteristic of all, olives (Olea europaea). Olives were an important crop in Greece from the Bronze Age and were well established in south Italy and Sicily by the eighth century BCE (Boardman 1976).
The ancients recognized nearness to the sea as important for growing olives. Theophrastus (HP 6.2.4) noted that the olive flourished no further than 300 stades from the sea (about 54 kilometres) and if it was found further inland – he specifies “more than five days' journey from the sea” - they were unfruitful (HP 4.4.1,5). The ancestor of these olive trees was the wild olive native to the Mediterranean, thought to have been domesticated first in the Levant with a possible second location for domestication in Spain (Zohary et al. 2012, 119, 121). The wild olive was distinguished from its domesticated relative in the way it reproduced. The wild olive grows by sexual reproduction from seed, the domesticated olive by vegetative reproduction, with new plants established from suckers or cuttings, often grafted on to wild olives (Zohary et al. 2012, 117). Theophrastus was not sure whether a wild olive could be tamed or a domesticated olive could turn wild; if it happened, it was uncommon (HP 2.2.12; 2.3.1).
    It is widely held that the domesticated olive was introduced to Italy and Sicily by Greek and Phoenician colonists from the second half of the eighth century. The colonists looked for sites with fertile fields where they could plant crops to feed themselves, the three most important crops being grain, grapevines and olive trees (Dunbabin 1948). The success of oleiculture in Sicily and south Italy is evident from exports. Diodorus (13.81.4) recorded that Akragas in Sicily was exporting olive oil to Carthage before the war with Hannibal and the Athenian poet Amphis was acquainted with the olive oil of Thuria (in Athenaeus 30b, 67b). Italian farmers were growing olives as a cash crop from the mid 3rd century BCE.  Pliny (HN 15. 1-3) measured olive production by contrasting prices in 249 BCE (10 asses for 12 pounds) with prices in 74 BCE (one as for 10 pounds). He also noted that olive oil was exported to the provinces 22 years later in 52 BCE, an indication that more olive oil was produced than could be used domestically.
The olive does not demand much work to grow as Vergil said, even if he was exaggerating (G. 2.420). The trees need good drainage and will not do well in swampy land. They were often planted on a slope, facing south or north depending on the circumstances – facing south to take advantage of the sun for as long as possible each day or facing north to provide shade for some time each day.

The praise of Italy

Varro, Vergil and the Elder Pliny each praised the fine climate enjoyed by Italy. Varro (Rust.1.2.3-7) attributed Italy’s climate to its being between Asia and the west and because it escaped the extremes of the frozen north and the hot south.  Italy, he declared, is more suited to cultivation than Asia and more temperate than farther inland in Europe. What useful product --and he was thinking of grain, wine and oil – fails to grow in Italy? Italy is “completely under cultivation” and is planted with so many trees that all of Italy is like an orchard (pomarium).
Vergil picks up the theme (G. 2. 136-76). Spring is incessant (assiduum) and summer extends to months where it doesn't belong (alienis mensibus). Italy bears “teeming fruit”, “Bacchus’ juice”, “olive-trees and pleasing herds.” He makes the astounding claim that in this wonderful climate twice each year herds give birth and trees bear fruit. This was certainly not generally true though occasional examples were known.
Pliny indulged in praise of Italy twice: near the beginning of his Natural History in book 3 (39-42) and at the end in book 37 (201-2). In book 3 he rhapsodized on the fresh and healthful climate, the fertile fields, the sunny hill sides. In book 37 (201-2) he proclaimed that there was no country so beautiful; the climate is healthful and mild. In an echo of Varro, Pliny says that the land occupies the most favourable position, because it lies midway between East and West.
In contrast, Columella began his work with an indication that all was not well in agriculture (R.R. preface). The soil and the climate were blamed for poor harvests although he believed that knowledge of farming and hard work with an appropriate amount of fertilizer would enable production equal to the past.  He advised farmers to inform themselves about what crops were suitable for their region and also to pay attention to weather signs. He lamented a decline of productivity in Italy, that land owners were using land for meadows and pasture or timber in place of vines and orchards (Columella 3.3.1).  Columella (3.3.4 cf. Varro 1.44.2) attributed this to carelessness:  people planted the worst kind of cuttings, did not nourish i.e. fertilize vines, and were careless about cultivating.
Neither Cato writing before the Roman Warm Period nor Palladius writing after made such claims for the Italian climate. For Cato, a farm will be successful if the landowner manages resources, including human resources, well.  Palladius had farms on Sardinia and in Italy near Rome; in a number of places he contrasted the time of year when certain tasks should be done in cold regions and hot regions with an indication that he himself had farmed in such extremes  (3. 25. 27, 4.10.15 and 8.3.2). The easiest way to get started with oleiculture was to find olive trees in woodlands or uninhabited places, cut the roots in cubit lengths and set them out in a nursery or orchard (3.18.6).  One imagines an olive tree deep in a woods or in a field near an old abandoned farm house. Olives were long lived and remarkably resilient so such olive trees must have been neglected for a long time.

Roman references to climate change 

a) Columella

Columella and Pliny both mention the possibility that climate had changed. The agricultural writer Saserna had read a treatise by the astronomer Hipparchus (c. 190 - c. 120 BCE) who had noted that some star positions did not match the observations of his predecessors and formulated the theory of the precession of the equinoxes (now called axial precession). For us the north celestial pole is very close to Polaris in Ursa Minor (the Little Dipper). For Hipparchus the nearest bright star was β Ursae Minoris, in the bowl of the Little Dipper and it was not very close. It takes 26,000 years for the celestial north pole to complete the cycle and come back to the starting point. Hipparchus speculated that at some future time the celestial poles would change position. Saserna concluded that this change in position had already happened and had resulted in dramatic climate change:

regions which before could not keep safe any shoot of the vine or olive which had been planted because of the constant violence of winter, are now rich with generous olive harvests and the vintage of Bacchus, now that the earlier coldness has been mitigated and become temperate (Columella 1.1.5).

   Saserna believed that he was observing the effects of climate change predicted by Hipparchus and that olives and vines were growing in his lifetime where they had not grown before. Columella placed him between Cato who died in 149 BCE and Varro (b. 116 BCE) whose work on agriculture was written in 37 BCE.  This presumably milder climate will have occurred between the second half of the 2nd century BCE to the first half of the 1st century and fits with the Roman Warm period.

b) Pliny

    Pliny (HN 15. 1.1-4) cited the late first century BCE historian Fenestella who had reported that the olive “did not exist at all in Italy, Spain, or Africa during the reign of Tarquinius Priscus” (in 580 BCE) “but now” (that is in the first century BCE) “it has reached even across the Alps and into the middle of Spain and Gaul.” This fits with Saserna’s observation that olives and vines grew in his day where the climate had become milder.
How we understand Fenestella depends on how the references to Italy, Spain and Africa are taken. The evidence of paleobotany demonstrates that Fenestella was wrong: olives had been cultivated in Spain from the 7th century BCE (Buxó 2008) and in Africa – specifically around Carthage --from the 6th century BCE (Lebreton et al. 2015). Breton (2009) argues that wild native olives in France near Marseille and in Africa from Morocco to Tunisia had been domesticated, though the Greeks and Phoenicians may have introduced other domesticated olives. I suggest that Fenestella was thinking of the intentional establishment of olive orchards by the Romans “across the Alps” and “the middle of Spain and Gaul”, quite possibly ignoring what was growing there.
Fenestella’s stipulation of a specific year (580 BCE) indicates that something changed and it has been suggested that it was the inclusion of Minerva in the Capitoline triad (cf. Varro ant. diu. fr. 18).  It would be natural to think that olives, the tree sacred to Athena, would have been introduced in that year in Minerva’s honour.
If I am right that Fenestella was implying a distinction between the coastal areas of Sicily and Italy and central Italy, between the coast of Spain and Gaul and the interior, and between Italy and the land on the other side of the Alps, then his statement that olives did not grow in the 6th century BCE in Italy, Spain and Africa would mean that they did not grow in the interior. 

Expansion and contraction of olive culture in the Mediaeval and Little Ice Age

Climatologists (Moriondi et al. 2013) have detected an expansion of olive culture in Europe to the north during the Mediaeval Climate Anomaly (900-1200 CE) when temperatures were warmer and a retreat to the south during the cooling of the Little Ice Age (1400-1900 CE). Moriondi et al. compare this to the expansion of olive growing mentioned by Pliny beyond the Alps into Gaul and in the interior of Spain.

Advice on growing the olive 

When the advice on olive culture in the various authors is compared, we can see a development from Cato to Palladius. Cato was writing for people who needed detailed instructions on planting and care of olive trees and the equipment needed for pressing to produce oil as well as the number of workers needed for various tasks. He listed the many uses of amurca, the side product of producing olive oil – the lees: as a fertilizer (Ag 36, 93), to keep down weeds and ward off pests (Ag. 91, 92, 95, 98), to coat containers for storing food (Ag 94, 101), and to protect leather, metal and pottery (Ag 97) as if his readers might fail to realize how useful amurca was.
Varro, in contrast, assumed that his readership would know what equipment was needed for processing olives and how grafting was done and did not need lengthy descriptions. He gave brief advice on the kind of soil preferred (Rust. 64), when to plant and prune and the harvest (Rust. 78-9). Vergil was born in Mantua in the north of Italy which was not famous for olive growing and as a result he was rather dismissive of olive culture (G. 2.420).
Columella was concerned that land owners were using land for meadows and pasture or timber in place of vines and orchards (R.R. 3.3.1). He remained convinced that fruit trees and vines could be grown successfully and in books 3 to 5 gave detailed and painstaking instructions for planting, cultivating, grafting and pruning.
Pliny read widely – or had work read to him – and gathered relevant material from past writers. His 15th book on fruit trees and vines is less how to grow olives than interesting things to know about them.
An intriguing reference to establishing an olive orchard is found in Palladius (3.18.6). The quick and easy way of growing olives was to dig up olive roots from forests or abandoned lands, cut them into lengths and plant them. Olives were notorious for their long life and their ability to sprout from apparently dead wood.  It appears that the owners had stopped caring for their olive orchards (and vineyards). There are other references to an agrarian recession from the second century on, possibly as the Roman Warm period came to an end (White 1970, 31).  We should also bear in mind that climate change does not affect temperature only; there may be too much or too little rain, causing flooding or drought and wreaking havoc on crops.

Conclusion

Olives are not only the typical crop of a Mediterranean climate, they are not grown successfully in other climates. They need the hot, dry summers and cool wet winters characteristic of this climate. The fact that they thrived further north in Gaul and central Spain suggests that the climate has changed.
They were domesticated from a native wild olive as early as the Neolithic era, were grown as a crop in the Greek Mediterranean in the Bronze Age and were brought to the west by Phoenician and Greek colonists where they bore fruit in settlements near the sea, in Sicily, south Italy, and the coasts of Spain, Gaul and north Africa.
Climate change between 100 BCE and 200 CE, the Roman Warm period, supported an expansion of olive growing to the north (on the other side of the Alps) and further inland (in the middle of Spain and Gaul). In addition to these references, passages in praise of Italy and its ideal climate may also reflect a change. In Columella’s time, farming was less successful than it had been, as he believed, because of poor techniques and insufficient fertilizer, and olive orchards were being replaced by meadows, pastures and timber stands which required less intensive work. By the fourth century CE olive trees could be found abandoned or surrounded by forests. In addition to a loss of agricultural skill, this giving up of olive orchards and other crops may be the result of cooler temperatures as the Roman Warm period came to an end.

 M. E. Irwin   irwin@utsc.utoronto.ca

Texts and translations of the Roman agricultural writers

Ash, H. B. 1977. Columella, De Re Rustica v. 1. London and Cambridge MA: Heinemann and Harvard University Press

Brehaut, Ernest. 1933. Cato the Censor on Farming. New York: Columbia University Press. New York.

Dalby, Andrew. Cato On Farming. De agricultura. A modern translation with commentary. 1998. Totnes, Devon: Prospect Books.

Fitch, J. G. 2013. Palladius. The Work of Farming. Totnes, Devon: Prospect Books.

Forster, E.S. and Edward H. Heffner. 1968 (v. 2) Columella, De Re Rustica. London and Cambridge MA: Heinemann and Harvard University Press.

Forster, E.S. and Edward H. Heffner. 1979 (v. 3). Columella, De Re Rustica. London and Cambridge MA: Heinemann and Harvard University Press.

Hooper, W.D. and H. B. Ash 1979. Cato and Varro, De re rustica. London and Cambridge MA: Heinemann and Harvard University Press.

Hort, A. 1916. (v. 1), 1926 (v. 2). Theophrastus. Enquiry into plants and minor works on odours and weather signs. London and Cambridge MA: Heinemann and Harvard University Press.

Jones, W.H.S. 1969, 1980. Pliny. Natural History vv. 20-23, 24-27. London and Cambridge MA: Heinemann and Harvard University Press.

Rackham, H. 1949. Pliny Natural History. v.1. London and Cambridge MA: Heinemann and Harvard University Press.

Thomas, R.F. 1988. Virgil. Georgics. 2 vols. Cambridge: Cambridge University Press.
Tilly, Bertha. 1973. Varro the farmer: a selection from the Res rusticae. London: University Tutorial Press.

Roman agriculture and climate change

Boardman, John. 1976. The olive in the Mediterranean: its culture and use. Phil. Trans. R. Soc. Land. B. 275, 187-196.

Buxó, Ramon. 2008. The agricultural consequences of colonial contacts on the Iberian Peninsula
in the first millennium B.C, Veget Hist Archeobot 17:145–154. DOI 10.1007/s00334-007-0133-7

Chen, L., Zonneveld, K.A.F. and Versteegh, G.J.M. 2011. Short term climate variability during the "Roman Classical Period" in the eastern Mediterranean. Quaternary Science Reviews 30: 3880-3891.

Dunbabin, T.J. 1948. The Western Greeks. Oxford and New York: Oxford University Press.

McCormick, Michael, Ulf Büntgen, Mark A. Cane, Edward R. Cook, Kyle Harper, Peter Huybers, Thomas Litt, Sturt W. Manning, Paul Andrew Mayewski, Alexander F. M. More, Kurt Nicolussi, Willy Tegel. 2012. Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence. Journal of Interdisciplinary History, 43.2, 169-220.

Moriondo, Marco, Giacomo Trombi, Roberto Ferrise, Giada Brandani, Camilla Dibari, Caspar M. Ammann, Marta Mariotti Lippi and Marco Bindi. 2013.  Olive trees as bio-indicators of climate evolution in the Mediterranean Basin. Global Ecol. Biogeogr. 22, 818–833. DOI: 10.1111/geb.12061.

Newton, Claire, Christine Lorre, Caroline Sauvage, Sarah Ivorra,  Jean-Frédéric Terral. 2014. On the origins and spread of Olea europaea L. (olive) domestication: evidence for shape variation of olive stones at Ugarit, Late Bronze Age, Syria—a window on the Mediterranean Basin and on the westward diffusion of olive varieties. Veget Hist Archeobot 23:567–575. DOI 10.1007/s00334-013-0412-4

Patterson, William Paul (1995), Stable isotopic record of climatic and environmental change in
continental settings, University of Michigan, OCLC 712737306, Thesis. Not seen.

Sarpaki, Anaya. 1992. “The Paleoethnobotanical Approach” in Berit Wells ed. Agriculture in ancient Greece. Stockholm: Proceedings of the Seventh International Symposium at the Swedish Institute in Athens, 61-76.

Spurr, M.S. 1986a. Arable Cultivation in Roman Italy 200 BC – AD 100.
Society for the promotion of Roman Studies, JRS monograph no.3

Spurr, M. S., 1986b. Agriculture and the 'Georgics'
 Greece & Rome, 33. 2, 164-187.


White, K.D. 1970. Roman Farming, Ithaca, New York: Cornell University Press.

Zohary, Daniel, Maria Hopf and Ehud Weiss. 2013. Domestication of Plants in the Old World. 4th  ed. Oxford: Oxford University Press.