Malaria and Rome: A History of Malaria in Ancient Italy (21 page)

¹⁴⁷ Dante Alighieri,
La Commedìa. Inferno. Canto
.46–9, ed. Lanza (1996):
Qual dolor fora, se delli spedali
|
di Valdichiana tra ‘l luglio e ‘l settembre
|
e di Maremma e di Sardinia i mali
|
fossero in una fossa tutta insembre
.

¹⁴⁸ Alexander (1984); Luchi (1981: 417–20), on the archaeology of the Val di Chiana in the territory of Chiusi, noted that Livy 5.36.3 indicates that at least part of it was exploited extensively instead of intensively (
latius possideant quam colant
); Dennis (1878: 294); Pinto (1982: 10, 17–18, 30).

Ecology of malaria

101

4. 5 C  

Roads and housing are good examples of factors which were very important at the local level. However, not all factors were so localized in their effects, above all climatic change. Huntington suggested in 1910 that the introduction of malaria to Italy occurred in the late third century  as a result of increasing aridity (and hence, drier summers) which created more favourable environmental conditions for
Anopheles
mosquitoes. Although that idea was interesting in principle, far less was known in 1910 about climatic change in the past and its causes and consequences than is known today. The question requires a fresh examination. It has already been noted that the earth’s average temperature is now approaching levels that were last attained in the Neolithic period, before 3000 , probably as a result of anthropogenic global warming in the last few years. In between, the climate was generally cool-er, but there were still periodic fluctuations of temperature within these lower levels. The effects of these temperature fluctuations can be analysed by studying periodic advances and retreats of the glaciers in the Alps, which have occurred throughout the Holocene. The time of the Roman Empire was mostly a warm period, relative to the periods immediately before and immediately afterwards. The results from the glaciers can be corroborated by various types of proxy data, for example the spread of viticulture into Roman Britain as demonstrated by the recent archaeological finds at Wollaston in the Nene Valley in Northamptonshire. The time of the Roman Empire was warmer than the period of the ‘Little Ice Age’,
c
. 1500–1800, which encompasses much of the data that are available for studying the distribution of malaria in Italy in the early modern period. Consequently the climate was more favourable for the spread of malaria in Italy during the Roman Empire than it was, say, in 1782, when malaria occurred all over Lazio, except at high altitudes, as shown by Bonelli’s map.¹⁴⁹

Climatic change, then, is a very important factor that creates the expectation of a wider distribution of malaria in Italy during the Roman Empire than during the early modern period. It is not surprising, as has already been noted (see Ch. 4. 2 above), that ¹⁴⁹ Huntington (1910: 672–5); Fraccaro (1919: 66–70); Röthlisberger (1986: 60–1, 70–4); Bianchi and McCave (1999); Brown and Meadows (2000).

102

Ecology of malaria

P. falciparum
malaria occurred in Umbria, far inland, by the fifth century . Temperature is very important in relation to malaria because of the requirements of the parasites for sporogony inside the mosquito. This developmental process, which is essential before the mosquito can infect anyone, takes only about 9 days at a mean temperature of 30°C, 10 days at 25°C, but up to 23 days at 20°C, in the case of
P. falciparum
. The time scale in the case of P. malariae
is even longer, about 20 days at 25°C, and 4–5 weeks at 20°C. Even though on the surface such temperature levels are not maintained for long periods in Europe (taking account of the drop in temperature that occurs every night), nevertheless the longevity of
P. malariae
infections in humans assured its survival until the next favourable transmission period came along, and there are many references to quartan fever in historical sources from Europe. In the case of
P. vivax
the process takes only 9 days at 25°C, but 30 days at 16°C. The slowing down of sporogony caused by low temperatures impedes the transmission of malaria because few adult mosquitoes actually live as long as 3 or 4 weeks. Hackett noted that over 50% of mosquitoes are dead after a week in Italy during the summer.¹⁵⁰

The scale of the temperature changes in the Roman period can be roughly estimated. One recent study suggested that the mean July temperature in the Arctic about 411 ± 70 years  (by C14

dating), at the peak of the Little Ice Age, was about 0.7°C lower than today. Wider studies have estimated a cooling of about 0.4–0.6°C during the Little Ice Age, explained by periodic variations in annual-mean radiation from the sun.¹⁵¹ Consequently it is likely that mean summer temperatures in Italy during the Roman Empire were a minimum of about 0.5°C higher (and quite possibly more) than the temperatures of the early modern period, which were already sufficient for
P. falciparum
malaria to be widely distributed in central and southern Italy. A temperature change of this magnitude may appear to be quite modest, but it is well known in ecology that small changes of this kind can have considerable effects on the distributions of living organisms. Moreover the effects of even small temperature changes would be most significant in geographical areas on the periphery of the distribution of
P. falciparum
, such as southern Europe, rather than in the tropics. Modern ¹⁵⁰ Hackett (1937: 67–9); Gilles and Warrell (1993: 111, 126–31).

¹⁵¹ Havström
et al
. (1995); Wigley and Kelly (1990).

Ecology of malaria

103

global warming is already creating more favourable conditions for the mosquito vectors of malaria and other diseases in many parts of the world.¹⁵² Some studies have argued that parts of the Roman period were even hotter, up to about 2°C warmer than the temperatures of the Little Ice Age in the early modern period, as well as being wetter than today. If so, the prospects for malaria during the time of the Roman Empire were that much better.¹⁵³

4. 6 A    

Increasing temperature favoured the spread of both
P. falciparum malaria itself and its vector mosquitoes in Italy during the time of the Roman Empire. There were other factors which were also of fundamental significance. Heat is good for malaria, but the mosquitoes still need to find suitable habitats for breeding sites. Human activity in the first millennium  unwittingly made a crucial contribution to the spread of malaria by altering the hydrology, geomorphology, and vegetation cover of lowland areas on a scale which transcended anything achieved in earlier periods. In Etruria the combination of the different types of evidence yielded by archaeological field surveys (e.g. the Tuscania and Veii surveys), palaeobotany, and palynology indicates that very substantial population growth occurred during the development of the Etruscan cities. This human population growth was supported by Mediterranean polyculture (the triad of cereals, olives, and vines), a new agricultural system which developed in central Italy for the first time in the Early Iron Age. The same sort of intensification of land use occurred in Latium as well.¹⁵⁴ Deforestation of hills and mountain slopes caused increased run-off of rainwater. This raised the water table and increased the chances of flooding in the lowlands and eroded soil to be redeposited as alluvial deposits in the lowlands. These areas of alluvial deposition were very likely to become marshy. This process happened all over Italy. The Greek colony of Metapontum in southern Italy is a well-studied example.

Archaeological investigations have shown that the water table rose ¹⁵² Epstein (2000); Patz and Reisen (2001). The alternative view advocated by Rogers and Randolph (2000) seems to totally ignore all the evidence for the existence of
P. falciparum malaria in the past in southern Europe, for example.

¹⁵³ Martinez-Cortizas
et al
. (1999); Reale and Dirmeyer (2000).

¹⁵⁴ Potter (1979: 74) summarized the explosion in site numbers in south-eastern Etruria; Barker (1988); Sallares (1991: 29–34) on the spread of new crops.

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Ecology of malaria

17. The Monti

Cimini, viewed from

the site of the Roman

villa at Lugnano in

Teverina. Most of

the redoubtable

ancient forest has

now disappeared.

Ecology of malaria

105

by more than a metre over the whole territory of Metapontum from the sixth to the fourth centuries . This was accompanied by extensive alluviation, which created marshy conditions suitable for
Anopheles
mosquitoes. The necropolis at Pantanello, whose very name indicates marshy conditions, outside Metapontum has yielded several skeletons which show signs of thalassaemia, an inherited genetic condition which confers a degree of resistance to P. falciparum
malaria. This constitutes indirect evidence for the likely existence and activity of
P. falciparum
in southern Italy as well as Sicily during the classical Greek period.¹⁵⁵

This is not the place for an extensive discussion of deforestation in Italy in antiquity. Suffice it to say that there were massive forests in Italy, which grew during the mid-Holocene climatic optimum, following the end of the last Ice Age. Delano Smith has suggested that even the Tavoliere in Apulia, a semi-arid region today, might have been substantially covered by forest in the early Neolithic period.¹⁵⁶ In western central Italy, which is much better watered than the Tavoliere, the climax vegetation in the absence of human interference undoubtedly would be large forests in many areas.

Many of these forests were broken up during the first millennium  by the demands of an increasing human population for open land for agriculture and by the ever-increasing demand of the Romans for timber. For example, Livy describes the Ciminian Forest. It was said to be so dense and forbidding
c
.310  that people were afraid even to approach it. Hardly anything is left of it today.¹⁵⁷ Pliny the Younger described the ancient woods of very tall trees on the Appennine mountains, above his estate at Tifernum in Umbria.¹⁵⁸ Theophrastus described very large forests in Latium at the end of the fourth century .¹⁵⁹ These forests were well watered ¹⁵⁵ Henneberg
et al
. (1992: 455) on thalassaemia. Their claim to have also found evidence for treponemal diseases such as syphilis in the skeletal remains from Metapontum remains controversial. Nevertheless malaria probably played a major role in the depopulation of the territory of Metapontum in the third century  described by Carter (1990).

¹⁵⁶ Delano Smith (1978: 53), cf. Caldara and Pennetta (1996).

¹⁵⁷ Livy 9.36.1–8, discussed by Meiggs (1982: 246) and Cornell (1995: 355–6); Pratesi and Tassi (1977: 49) described the remnants of the Ciminian Forest.

¹⁵⁸ Pliny,
Ep
. 5.6.7:
montes summa sui parte procera nemora et antiqua habent
.

¹⁵⁹ Theophrastus,
HP
5.8.3 and 2, ed. Amigues (1993): Ó d† t0n Lat≤nwn πfudroß p$sa: ka≥ Ó m†n pedein¶ d3fnhn πcei ka≥ murr≤nouß ka≥ øxu¶n qaumast&n: thlikaıta g¤r t¤ m&kh tvmnousin ¿ste e”nai dianek0ß t0n Turrhn≤dwn ËpÏ t¶n trÎpin: Ó d† ørein¶ pe»khn ka≥

ƒl3thn. tÏ d† Kirka∏on kalo»menon e”nai m†n £kran Ëyhl¶n, dase∏an d† sfÎdra ka≥ πcein drın ka≥ d3fnhn poll¶n ka≥ murr≤nouß . . . tÏn d† tÎpon e”nai ka≥ toıton nvan prÎsqesin ka≥

prÎteron m†n oˆn n[son e”nai tÏ Kirka∏on, nın d† ËpÏ potam0n tinwn proskec0sqai ka≥

106

Ecology of malaria

and had taller trees than the forests of southern Italy (although not as tall as those of Corsica). The lowland forests of bay, myrtle, and beech contained old trees tall enough to span the length of the keel of an Etruscan ship, while there were upland forests of fir and silver fir. The extant text seems confused, since beech (
Fagus silvatica
, øx»h), which dominated the summits of the mountains of Lazio in the early modern period, belongs in the upland forests. If there were any beech forests in the lowlands of Latium
c
.300 , they were relics of previous colder periods, which were doomed to extinction during the warmer climate of the Roman Empire.¹⁶⁰

Theophrastus’ description of the region around ancient Circeii shows that he was aware of ongoing environmental change in the form of the alluviation which was thought to have attached Circeii, regarded in antiquity as once having been an island, to the mainland of Italy. Monte Circeo is regarded by modern geologists as e”nai ]∫Îna. t[ß d† n&sou tÏ mvgeqoß per≥ øgdo&konta stad≤ouß . . . t0n g¤r ƒn t∫ Lat≤n7

kal0n ginomvnwn Ëperbol∫ ka≥ t0n ƒlat≤nwn ka≥ t0n peuk≤nwn—me≤zw g¤r taıta ka≥

kall≤w t0n ∞Italik0n. (The whole territory of the Latins is well-watered; the plains contain forests of bay, myrtle, and wonderful beech. They fell timbers of it so long that they span the entire length of the keel of an Etruscan ship. The hills have forests of fir and silver-fir . . . The so-called Circaion is an elevated promontory, but it is densely wooded and has oak trees, a lot of bay, and myrtle. The land surrounding the Circaion has been created recently by sedimentation from certain rivers, but the Circaion was formerly an island. The island was about eighty stades in circumference . . . silver-fir and fir grow extremely tall in Latium and are taller and finer than in southern Italy.).