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Journal of Archaeological Science 38 (2011) 925e933

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Journal of Archaeological Science

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Stable isotope analysis of a medieval skeletal sample indicative of systemicdisease from Sigtuna Sweden

Anna Linderholm a,1, Anna Kjellström b,*

aArchaeological Research Laboratory, Department of Archaeology and Classical Studies, Stockholm University, 106 91, Stockholm, SwedenbOsteoarchaeological Research Laboratory, Department of Archaeology and Classical Studies, Stockholm University, Lilla Frescativägen 7, SE-106 91, Stockholm, Sweden

a r t i c l e i n f o

Article history:Received 1 July 2010Received in revised form22 November 2010Accepted 25 November 2010

Keywords:Systemic diseaseLeprosyTuberculosisSocial classesDietStable isotopesCarbonNitrogenSulphur

* Corresponding author. Tel.: þ46 8 161287; fax: þE-mail address: anna.kjellstrom@ofl.su.se (A. Kjell

1 Present address: Department of Archaeology, DuDurham DH1 3LE, United Kingdom.

0305-4403/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.jas.2010.11.022

a b s t r a c t

In Sigtuna, Sweden, several medieval cemeteries have been excavated, from which approximately 800skeletons have been excavated and analysed. Archaeological finds and anthropological analyses haveexposed social differences between the cemeteries. Stable isotope analyses have shown that theinhabitants of the town consumed a mixed diet. Significant differences in dietary patterns between thecemeteries may be related to social stratification.

In the outskirts of a churchyard excavated in 2006, bone changes showing systemic inflammatorydisease indicative of leprosy were observed in six individuals. The burial location suggests that theaffected belonged to a lower social stratum. Bone samples were taken from these six individuals, 19 otherhuman skeletons and five animals from the same cemetery for analysis of the stable isotope compositionof carbon (C), nitrogen (N) and sulphur (S).

The results showed no significant differences in d13C and d15N values between the groups, i.e. theseemingly healthy humans and the humans affected by severe inflammatory disease appear to have hadsimilar diets. Nor was a significant difference observed in d34S data between the six affected individualsand the rest of the sample, implying that no difference in origins could be observed between the twogroups studied. However, a comparison between the present study and the previous analysis resulted insignificant differences in carbon values.

Based on the results obtained in this investigation it is suggested that if a dietary difference existedbetween people in the outskirts of a cemetery (for example those suffering from leprosy) and peopleburied in higher ranked regions, it was not a difference in food source but rather in other parameters.Instead dietary differences and possibly social variations are demonstrated between cemeteries. Theresults from the present study highlight the hierarchical arrangements of social classes in the earlymedieval society.

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1. Introduction

Individuals with leprosy have been documented in Sigtuna. Ina grave excavated in 1995 associated with the church known as“Church 1” (Kjellström, 2005), an affected individual was identified.The grave was located in the periphery of the churchyard. Theplacement of the graves is in line with coeval Scandinavian burialregulations (for example the Norwegian law Eidsivatingslagen),which assigned the areas most distant from the church to the poor

46 8 164476.ström).rham University, South Road,

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or outcasts (Gejvall, 1969: Daniell, 1997). A similar location forpeople with skeletal changes of leprosy, showing their low socialposition in society, has been documented in medieval Lund, in thesouth of Sweden (Arcini, 1999).

The present study considers the diet and origins of six individ-uals also discovered in the outskirts of a medieval churchyard inSigtuna. Skeletal changes indicate that the group had suffered fromsystemic disease. Their burial location implies that these individ-uals also belonged to a low social stratum. Previous studies haveshown that dietary differences, most likely related to social hier-archy, already existed between groups during the initial phase ofthe town’s establishment (Kjellström et al., 2009). Althoughknowledge of the current church and churchyard is low it was mostlikely not a formal nursing institution. (A hospital was first estab-lished in Sigtuna in A.D. 1287, around the time of the abandonment

A. Linderholm, A. Kjellström / Journal of Archaeological Science 38 (2011) 925e933926

of the excavated churchyard [Kjellström andWikström, 2008]). Thehypothetical notion that these individuals were treated differentlyor that they came from another region is tested in this paper.

2. The history of Sigtuna

Sigtunawas founded in the 10th century AD on the shore of LakeMälaren, near the coast of the Baltic Sea in east central Sweden,(Fig. 1). Approximately 800 skeletons from several medievalcemeteries in the town have been analysed to date. The graves aredated to three burial phases; signifying the establishment of thetown (Phase 1 c. 900e1100), its peak of prosperity (Phase 2 c.1100e1300), and its decline (Phase 3 c. 1300e1530) (Kjellströmet al., 2005; Wikström, 2008).

During the Viking Age Lake Mälaren was still a bay of the BalticSea, and seagoing vessels could sail up it far into the interior ofSweden. However, around 1200 AD the bay became a lake due topost-glacial rebound and today the lake’s surface averages 0.7 mabove sea level.

Sigtunawas from the beginning a highly stratified society wherethe first Christian kings both planned the topography of the townand controlled the population living within its limits (Tesch, 1990,2000, 2001; Zachrisson, 1998; Kjellström et al., 2005). Wide-ranging contact with other European countries is demonstrated inartefacts and designs from northern Germany, Denmark, England,Holland, France, Belgium, Germany, Byzantium and Kiev (Karlsson,1989; Larsson, 1990; Roslund, 1990, 2001). Although smallcompared to contemporary international towns, Sigtuna had anurban character, lacking agrarian constructions such as stables orbarns (Högrell, 1990; Petterson, 1990). The surrounding country-side provided the citizens with meat. In the cultural layers thezooarchaeological data contained bone remains from domesticanimals such as cattle, sheep, goat and pig (Hårding, 1990) as wellas game animals, wild fowl and fish (Jonsson, 1989; Hårding, 1990;Vretemark, 1997). In addition to the most basic crops, fossil plantremains show that a diversity of vegetables, fruits and herbs werecultivated (Hansson, 1997). Stable isotopic analyses have verifiedthat the diet contained a combination of both terrestrial andmarineprotein but was generally predominantly terrestrial in origin(Kjellström et al., 2009). Variations in the intake of vegetableprotein, most likely socially motivated, were discernable between

Fig. 1. Map of Sweden and Sigtuna with the location of some of th

groups (Kjellström et al., 2009). Significant differences (P < 0.001)in nitrogen values between women at the burial ground Nunnan(d15N mean ¼ 10.73&, s.d. ¼ 1.52) and the (supposedly high status)women at a churchyard called “Church 1” (d15N mean ¼ 13.06&,s.d. ¼ 0.68) were observed. One of the samples (Church 1, phase 2)was contemporary with the skeletal assemblage in the Humle-gården block presented below.

3. Stable isotope analysis in archaeology

Stable carbon and nitrogen analysis is a well-establishedmethod for examining prehistoric diet (Schwarcz and Schoeninger,1991; Katzenberg, 1992; Sealy, 2001; Kellner and Schoeninger,2007; Linderholm, 2008; Eriksson et al., 2008; Linderholm et al.,2008a and 2008b). The central principle behind this method isthat “you are what you eat”, namely that skeletal tissue is formedfrom components in the diet. Themain protein in the skeletal tissueis collagen, and it is made up of amino acids which are synthesiseddirectly from the diet. Analysis of this collagen will consequentlyreflect an individual’s diet during the 10e to 15 years prior to death(Fischer et al., 2007). Collagen can survive in the skeleton forthousands of years under good preservation conditions(Ovchinnikov et al., 2001; Götherström et al., 2002; Smith et al.,2005). Several experimental studies have shown that it is mainlythe protein portion of the diet that is reflected in collagen isotopicdata (Ambrose and Norr, 1993; Howland et al., 2003; Jim et al.,2004; Tiesze and Fagre, 1993). The carbon isotope ratio, d13C,distinguishes protein from different sources; it can distinguishbetween protein from terrestrial or freshwater environments andprotein from marine environments, or C4 plants from C3 plants(Schoeninger and DeNiro, 1984). C4 plants are found in tropical orsubtropical environments and are not thought likely to havecontributed to the diet in medieval Sigtuna. This means that allterrestrial protein is considered to derive from C3 plants in thisstudy. The nitrogen isotope value, d15N, on the other hand, willincrease for each step in the food chain by approximately 3&, andone can thus discriminate between trophic levels in the food web(Minagawa and Wada, 1984; Schoeninger and DeNiro, 1984). Boththe carbon and the nitrogen isotopic values are measured againstinternational standards and are expressed in per mil, &, i.e. partsper thousand.

e excavated churchyards (the Humlegården block ¼ Church 2).

A. Linderholm, A. Kjellström / Journal of Archaeological Science 38 (2011) 925e933 927

4. Sulphur analysis as a tool for provenience determination

During the last ten years analysis of the stable isotopes of sulphur(d34S), has successfully been applied to several archaeological studies(Richards and Hedges, 1999; Richards et al., 2001, 2003; Leach et al.,2003; Craig et al., 2006; Privat et al., 2002; Linderholm et al., 2008aand 2008b; Fornander et al., 2008; Nehlich and Richards, 2009;Nehlich et al., 2010). Plants derive the majority of their sulphurfrom the soil and the soil’s d34S signal is derived from the localbedrock. A small part of the sulphur intake will be derived fromatmospheric depositions and microbial activities in the soil but toamuch lesser extent. Terrestrial sulphur isotopic conditions thus varydependingongeological setting. The d34S values of sedimentary rocksrange from �40 to þ40&, European granitic rocks have d34S valuesthat range from �4 to þ9&, mafic rock d34S values are close to 0&,and metamorphic rocks exhibit d34S values between �20 andþ20&(Krouse, 1980; Faure and Mensing, 2005). By comparison, the d34Svalue for the oceans are rather uniform, averaging 21&, with marinevegetation having d34S values between þ17& and þ21& (Petersonand Fry, 1987). As a result of the reduction of sulphate ions (SO4

�) tohydrogen sulphide (H2S), the d34S values in freshwater systems aremuch more dispersed ranging from �22 to þ20& (Krouse, 1980;Faure and Mensing, 2005). Because of this terrestrial and fresh-water d34S values vary far more than marine ones. The isotopic frac-tionation between food and consumer is relatively small (�1& toþ2&), meaning that the d34S value in bone reflects the sulphurisotopic composition of the dietwhich in turns reflects the geology ofthe food origin (Peterson et al., 1985; Bol and Pflieger, 2002; Sharpet al., 2003; Richards et al., 2003; Fraser et al., 2006; Buchardt et al.,2007; Nehlich and Richards, 2009). Thus any detected variation inthe d34S data could indicate geographical origins of the food andwiththis information migration patterns may be elucidated.

5. Materials

In the summerof 2006Sigtunamuseumconductedanexcavationof the southern parts of the Humlegården block (Wikström, 2008).The excavation covered 160m2 and included 220 east-west orientedgraves with 227 skeletons. The same churchyard has been investi-gated in 1991 when 99 skeletons were documented (Kjellström,2005). The name of the church is unknown, but in the earlierinvestigation it was called Church 2, which is used henceforthin this study. The skeletons exhibited a variety of skeletal changesand in comparison with other cemetery assemblages in Sigtuna,

Fig. 2. (a) The feet of an adult woman (Case 2); (b) Acroosteolysis of the right fifth metatarsright side; (d) A “pencil and cup” deformity of the right first metatarsal and proximal phal

significantly higher frequencies of several pathologies wereobserved (Kjellström and Wikström, 2008). Six skeletons showedsigns of severe systemic disease not observed in the rest of theskeletal collection (Kjellström, 2010). Two of three individuals withpreserved facial bones demonstrate signs of rhinomaxillaryremodelling. Five of the affected exhibit bilateral periosteal newbone formation, severe remodelling of the phalanges of the feet andpencil shaped metatarsals. Additionally one of the individuals hadlytic lesions confined to the lumbar spine, which had resulted in anangular kyphosis. In at least two individuals lepromatous leprosyand tuberculosis could be confirmed respectively. Although theremaining four skeletons exhibited severe bone atrophy in their feet(and three of them showed mild bone alterations in their hands)characteristic of leprosy, other diseases could not be ruled out.

6. Methods

6.1. Osteological methods

The skeletal assemblagewas sexed and aged according to currentstandard anthropological techniques (Moorrees et al., 1963a and1963b; Phenice, 1969; Stloukal and Hanáková, 1978; Stewart, 1979;Novotný, 1982; Brothwell, 1981; Lovejoy et al., 1985; Meindl andLovejoy, 1985; Pearson, 1917-19 in Bass, 1987: 219; Ubelaker, 1989;Brooks and Suchey, 1990; Buikstra and Ubelaker, 1994; Scheuerand Black, 2000; Bruzek, 2002). The measurements were takenaccording to definitions set up by Buikstra and Ubelaker (1994).Differential diagnosis of leprosy was carried out following criteriapresented by Andersen and Manchester (1992); Andersen et al.(1994); Aufderheide and Rodríguez-Martín (1998); Ortner (2003);Resnick and Niwayama (1988).

In addition to the six skeletons with bone changes associatedwith systemic disease a control group of 19 adult individuals ofboth sexes (ten women and nine men) were picked out. Except fordegenerative changes of the joints and signs of trauma on some ofthe individuals, the skeletons in the control group displayed nosigns of systemic infectious diseases (Fig. 2). In addition, asa reference, bone samples were taken from cattle (Bos taurus), cat(Felis catus), pig (Sus domesticus) and pike (Esox lucius).

6.2. Bone sampling and collagen extraction

The long bones used in this part of the study were first cleanedand bone powder was then obtained by use of a dentist’s drill.

al; (c) A “pencil and cup” deformity of the first metatarsal and proximal phalanx on theange the left side; (e) Acroosteolysis of the left fifth metatarsal.

A. Linderholm, A. Kjellström / Journal of Archaeological Science 38 (2011) 925e933928

Collagen was extracted from skeletal elements according to Brownet al. (1988) in a designated bone laboratory at the ArchaeologicalResearch Laboratory, StockholmUniversity. The samples weredemineralised in a 0.25M HCl solution for 48 h at room tempera-ture, filtered and washed twice with deionised water througha glass filter. After an addition of 0.01M HCl, the samples wereincubated at 58 �C overnight in order to dissolve the organicmaterial. The dissolved organic residue was then filtered andwashed with deionised water through an ultrafilter (30,000MWCOAmicon Ultra-15 Centrifugal filter device (Millipore)), removingparticles of less than 30kDaltons. Particles larger than 30kDaltonsare likely to be undamaged collagen. The residual solvent was thentransferred to a 2 ml Eppendorf tube and frozen at �80 �C, afterwhich the sample was freeze-dried and weighed.

For the d13C and d15N measurements approximately 0.5 mg ofcollagen was weighed into tin capsules for combustion in a PDZEuropa ANCA-GSL elemental analyzer interfaced to a PDZ Europa20e20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK).This step was performed at the UC Davis Stable Isotope Facility,Department of Plant Sciences, UC Davis, California, USA. Precisionwas�0.1& for d13C and�0.4& for d15N. For the d34Smeasurementsapproximately 5 mg of collagen was used. The analyses werecarried out at Iso-Analytical Limited, Crewe, UK using the EA-IRMStechnique. Analytical precision was within �0.3& for the d34S.

A two-sample t-test was used for comparison of stable isotopevalues between samples. Statistical analysis was conducted using

Table 1Results of the stable isotope analysis of human bone samples from the Humlegården blo

Lab # Id no. Sex d13C (&) %C d15N (&)

1 3013 F �20.4 36.4 14.32 3014 F �20.9 39.6 13.13 3029 F �21.2 34.1 11.64 3045 F �20.8 38.9 145 3064 M �21.2 33.5 13.96 3068 M �20.5 34.4 14.4

7 3077 F -20,6 37,8 11,5

8 3092 ? -20,7 37,9 14,3

9 3093 M -21 39,9 13,8

10 3097 M �20.3 36.9 14.311 3134 M �21.1 36.1 13.5

12 3159 M -19,3 38,7 12,7

13 3195 F �20.3 34.1 14.214 3196 F �20 6 37.5 14.215 3225 M �21.3 37.6 11.216 3227 M �20.4 37.1 11.617 3233 M �20.4 38.3 11.218 3247 F �20.9 37.2 14.819 3250 M �19.3 35.4 1320 3275 F �20.7 35.1 13.821 3281 M �20.2 36.8 14.6

22 3320 ? -20,3 37 13

23 3336 F �20.6 37.1 14.8

24 3401 M -19,5 36,1 12,7

25 3439 F �19.4 346 9.6Mean �20.5 1.2S.d. 0.6 1.4

SPSS for windows (version 16.0) and P values <0.05 were consid-ered significant.

7. Results

7.1. Preservation

Post-mortem degradation of bone occurs in at least three ways:chemical deterioration of the organic phase, chemical deteriora-tion of the mineral phase and microbiological attack on the overallcomposition (Collins et al., 2002; Hedges, 2002). In addition,several parameters are involved in the loss of collagen from bonematerial, the main ones being time, temperature and pH (Collinset al., 2002; Hedges, 2002). In order to control for diageneticallyaltered bone we used the parameters put forward by DeNiro(1985), Ambrose (1990), van Klinken (1999), which require thatthe C/N ratio should fall into the range 2.9e3.6, the collagenshould be 15.3e47% carbon and 5.5e17.3% nitrogen by mass, andthe collagen yield should be greater than 1%. The sulphur valueswere verified using the newly established criteria based on C/S andN/S ratios (Fornander et al., 2008; Nehlich and Richards, 2009).Two samples out of the 25 were discarded due to low C/N ratios.None of the samples were disregarded due to the C/S or N/S ratios(Table 1). None of the samples from faunal remains were discarded(Table 2).

ck 2008. Individuals affected by systemic disease are marked in grey.

%N C/N d34S(&) % S C/S N/S

14.6 2.9 4.3 0.24 397 13714.1 3.3 6.6 0.25 418 12813.1 3 9 0.24 376 12414.7 3.1 6.8 0.29 358 11612.1 3.2 2.6 0.29 310 9613.4 3 5.2 0.32 287 96

11,7 3,8 7,3 0,27 380 101

14,7 3 3,2 0,27 376 125

14,4 3,2 9,8 0,24 451 140

13.8 3.1 7.4 0.3 329 10613.7 3,1 4.7 0.27 362 118

14,1 3,2 11,7 0,26 401 126

13.5 2.9 5.1 0.44 207 7014.7 3 5.9 0.25 398 13414 3.2 11.6 0.27 376 12014.1 3.1 8.7 0.3 331 10814.5 3.1 9.5 0.34 301 9814 4 3 6.4 0.25 401 13314.3 2.9 8.7 0.33 290 10114.4 2.8 4.4 0.32 296 10414.8 2.9 7 0.25 385 133

14,8 2,9 8,4 0,26 376 129

13.8 3.1 5.1 0.29 339 108

14,6 2,9 8 0,26 371 129

13.9 2.9 7.8 0.28 327 11372.4

Table 2Results of the stable isotope analysis of animal bone samples from the Humlegårdenblock 2008.

Lab # Species d13C(&)

%C d15N(&)

%N C/N d34SV-CDT(&)

% S C/S N/S

26 bos �22.5 41.2 5.2 14.9 3.2 1.4 0.28 390 12127 felis �22.1 41.1 10.7 14.4 3.3 5.6 0.32 343 10328 esox �20.4 36.5 13.1 14.2 3 6.7 0.6 161 5430 sus �21.9 37.9 9.5 15.5 2.9 6.5 0.28 363 127

Fig. 4. Scatter plot showing the distribution of d13C and d34S values for skeletonsindicative of leprosy and a control group from the Humlegården block.

A. Linderholm, A. Kjellström / Journal of Archaeological Science 38 (2011) 925e933 929

7.2. Isotope data

In all, the carbon and nitrogen values from the individuals withbone changes did not differ significantly from nearby skeletons inthe control group from the same cemetery (Table 1, Fig. 3). The dietseems to have been rather homogenous with mainly terrestrialprotein seen in the carbon values (d13C mean ¼ �20.47&,s.d. ¼ 0.57). The standard deviation of 0.57 is however slightlyhigher than the postulated standard deviation of 0.3 said torepresent a population with a homogenous diet according to Lovellet al. (1986), but low enough to infer a fairly homogenous diet. Nosignificant differences can be detected between the affected andnon-affected concerning either carbon (t (21) ¼ �1.283, P ¼ 0.213)or nitrogen (t (21) ¼ �0.084, P ¼ 0.934) values. When looking atmales versus females no significant differences can be seen ineither the d13C (t (19) ¼ 0.620, P ¼ 0.543) or d15N (t (19) ¼ �0.489,P ¼ 0.631) values. There is however a strong indication of a regularanimal protein diet, shown in the high values of nitrogen (d15Nmean ¼ 13.19&, s.d. ¼ 1.38) (Table 1, Fig. 3).

The sulphur data for the combined sample (d34S mean ¼ 7.11&,s.d. ¼ 2.41) fits in general with the surrounding bedrock signal(granite has a range from �4e9&). When divided into individualsaffected (d34S mean ¼ 8.23&, s.d. ¼ 3.14) and not affected (d34Smean ¼ 6.80&, s.d. ¼ 2.18) with systemic disease no significantdifference is seen between the two groups (t (21) ¼ �1.186,P ¼ 0.249) (Fig. 4).

When looking at the males (d34S mean ¼ 7.90&, s.d. ¼ 2.73)versus the females (d34S mean ¼ 6.33&, s.d. ¼ 1.45) no significantdifference can be seen either (t (19) ¼ 1.565, P ¼ 0.134). (Table 1).

The animals analysed show a range of d34S values from 1.44 to6.74& (Bos 1.4&, Felis 5.6&, Esox 6.7& and Sus 6.5&). They areused as a baseline, a local point of reference for the interpretationsof the sulphur values (Table 2, Fig. 4).

Fig. 3. Scatter plot showing the distribution of d13C and d15N values for skeletonsindicative of leprosy and a control group from the Humlegården block.

Attempts to reconstruct the diet for the same period in Sigtunahave been performed previously in 2005 (Kjellström, 2005;Kjellström et al., 2009). A comparison between the contemporaryassemblage from the previous study (of Church 1) and the presentanalysis resulted in significant differences in carbon values(P < 0.001) but not in nitrogen values (Fig. 5).

8. Discussion

8.1. Human diet during the medieval period in Europe

In comparison with other dietary studies performed on similardatedmaterials across Europe this set of dietary data conforms well(Privat et al., 2002; Polet and Katzenberg, 2003; Bayliss et al., 2004;Müldner and Richards, 2007; Fornaciari, 2008). In an early study ofan Anglo-Saxon cemetery, Privat et al. (2002) showed that the dietwas based on terrestrial food with carbon values ranging from�20.7& to �19.1&. The nitrogen values confirmed this, havinga range of 8.4&e12.8&. It is clear though that some of the indi-viduals studied here were supplementing their diet with somefreshwater fish. Privat and colleagues also tested their data set toexamine if there were any differences in dietary compositionbetween the sexes, but no such difference was observed (Privat

Fig. 5. Scatter plot showing the distribution of d13C and d15N values for the 2008sample from the Humlegården block (Church 2) and a control group from anothercemetery (Church 1) in the 2005 analysis.

A. Linderholm, A. Kjellström / Journal of Archaeological Science 38 (2011) 925e933930

et al., 2002). They detected a stronger input of freshwater fish in the“poor” group relative to the “wealthier” population. When a medi-eval monastic community from the coast of Belgiumwas examined,the mean values were �19.1 � 0.46& and 11.1 � 0.92& for carbonand nitrogen respectively. The carbon isotope values were indica-tive of a terrestrial based diet. Once again the nitrogen isotopicvalues are high and can be explained by an input of freshwater fishor other marine products (Polet and Katzenberg, 2003).

8.2. Sulphur isotope values from Sigtuna and other parts of Sweden

Since the number of investigations using d34S on archaeologicalmaterial is low, there are not that many data sets to compare thesedata to. The sulphur values obtained here show a rather dispersedset of d4S values ranging from 2.6 to 11.7&, with a mean ¼ 7.1&,s.d. ¼ 2.4. The d34S values are higher compared to two sets ofpreviously published d34S values from other places in Sweden; fromBirka (in close proximity to Sigtuna) mean ¼ 5.2&, s.d. ¼ 2.5(Linderholm et al., 2008a) and from Björned in the north of Swedenmean ¼ 5.4&, s.d. ¼ 3.4 (Linderholm et al., 2008b). The interpre-tation of the human d34S values is that they mostly fit with thesurrounding geological signal stemming from the granite bedrock(21 individuals fall between �4 and 9&). However there are someoutliers that may well be from other places. There are for exampletwo individuals with d34S values above 11& (11.6 and 11.7&). Theyboth fall well above the granite signal for the surrounding area andcould possibly be from a different region altogether. Based on theseresults we cannot say that all humans buried at the cemetery werelocal. It is interesting to note that the individuals with the highestsulphur value represent both groups, this is also true for the indi-viduals with the lowest sulphur values. This supports the inter-pretation that there is no geographical difference between the twogroups investigated here.

None of the 23 remaining human samples or any of the animalsamples were disregarded due to low C/S and N/S ratios (Fornanderet al., 2008; Nehlich and Richards, 2009). Accordingly to Nehlichand Richards (2009). Three of the samples showed a lower C/Sratio (207, 287 and 290) and four samples showed a lower N/S ratio(70, 96, 96, and 98) than would be expected. All of these values arehowever in the range suggested by Fornander et al. (2008). Forthese values the indications for collagen preservation arewithin thedocumented ranges and are thought to be reliable (Table 1).

Animal d34S values are traditionally used as a “local” reference.In this study we have the cat (5.6&) and the pig (6.5&) asa terrestrial reference, and amarine reference from the fish. Aquaticanimals have a different sulphur source and the 34S value for thefish can thus be different because of this (6.7&). The very limitedamounts of animals analysed in this case study severely weakensthe construction of a local baseline/signal, however they aresuggestive of a local signature. The pig analysed in this investiga-tion could very possibly be a domestic one and if so, might havebeen fed on human food waste. This would to some extent explainthe d34S values and the higher d15N value. The pigs would mostlikely have been fed some fish scraps if fish were consumed at thesite. Furthermore, it is possible that the pigs fed on plants affectedby sea-spray aerosols as a result of, for example, a higher exposureto wind (cf. Angerbjörn and Pehrson, 1987). Only very small tracesof a sea spray effect might be observed in our samples; it mightexplain the pig and some of the range of our d34S values. Since wecannot detect it in any profound way it is unlikely to have a largeeffect on or data. The only “non-local” value among the animalstested seems to be the cattle sample (1.4&). Excluding the cattlesample would give the animals a d34S mean ¼ 6.3&, s.d. ¼ 0.6. This“local” signal fits very well with the mean value obtained for thehuman individuals tested (d34S mean ¼ 7.1&). Given that the

isotopic fractionation between food and consumer is relativelysmall (�1& to þ2&) and the surrounding bedrock signal (granitehas a range from �4 to 9&) the sulphur signals obtained in thisstudy appear to indicate a local origin.

The sulphur values show no difference between individualsaffected by systemic disease and non affected individuals, nor doesthere seem to be any difference between the different sexes. Thiswould indicate that there is no division between the affected andnon-affected individuals.

8.3. Disease, religion and diet during the medieval period

In a study from 2004 Bayliss et al. investigated a medievalcemetery in Norwich. It is a cemetery where healthy individuals areburied next to individuals affected by leprosy, thus resembling thecemetery investigated in this study (Bayliss et al., 2004). Eventhough the focus of the paper was on the radiocarbon dates inconjecture with dietary offsets, similarities may be discernedbetween the isotopic data obtained in this study and the ones fromthe Humlegården block. At Norwich the carbon values ranged from�20.9& to �17.0& and the nitrogen values from 9.8& to 13.5&.There seems to be no difference between the individuals showingsigns of leprosy and those who do not. The sample from theHumlegården block has a much higher d15N signal than all the datapresented in prior studies, and the amount of freshwater fish orother 15N-rich food digested seems fairly high. However, isotopicvalues in accordance with those from Humlegården were obtainedin an investigation performed by Müldner and Richards in 2007 ona medieval English population (Müldner and Richards, 2007). Inthis material the religious impact on the diet is strongly demon-strated and can be compared to our data set. Their study is based onstable isotope analysis on populations from three different medi-eval sites in Northern England: a friary, a mass grave, and a ruralhospital. All of these new sites differ from prior investigationsperformed on archaeological populations in one aspect; they alldemonstrate enriched d15N values in combination with terrestrialcarbon signals. The explanation given by Müldner and Richards forthis phenomenon is that what is being measured is actually theimpact of medieval fasting regulations. The results also point to thefact that there was little difference in diet between different socialgroups. There is a slight difference within the populations; thepriests and patrons have higher nitrogen values than the rest.Basically what we can see in this study is an increase in freshwaterfish consumption in thesemedieval populations regardless of socialstanding. The stable isotope values from the three sites range from�20.6& to �18.1& for carbon and from 10.5& to 14.9& fornitrogen (Müldner and Richards, 2007). These values are verysimilar to the values obtained in the current study and the expla-nation for the high nitrogen values in combination with extremeterrestrial carbon values may be the same. Hence, what we areseeing in our data set is most likely evidence for medieval fastingpractices.

So, in order to explain the high d15N ratios seen in this study incombination with totally terrestrial carbon signals one has to lookat some possible explanations. These could be a diet based onfreshwater resources, migrating birds, suckling animals or on porkfrom animals that had themselves consumed large quantities ofanimal products (Privat et al., 2002; Rubenstein and Hobson, 2004;Jay and Richards, 2006). The latter scenario seems rather unlikelybased on data from the single pig analysed and thus cannot accountfor the high d15N ratios obtained. Discoveries of bone debris frommigrating birds and juvenile livestock have been made in Sigtunabut the explanation of a high input of freshwater fish in the dietseems far more plausible. It has been shown in prior studies thata large part of the diet in medieval populations was based on

A. Linderholm, A. Kjellström / Journal of Archaeological Science 38 (2011) 925e933 931

freshwater fish (Privat et al., 2002; Polet and Katzenberg, 2003;Müldner and Richards, 2007). In a recent paper by Grupe et al.(2009) stable isotope analysis was performed in order to evaluatethe brackish water aquatic food web. Here they clearly show thatfreshwater fish can be depleted in their d13C values. They alsoobserved raised d15N values for carnivorous, top-consuming fishspecies (i.e. cod), which could explain the high d15N values obtainedin this study. This is also corroborated with the fact that religiousbeliefs dictated that fish should be eaten during the fast on certaindays (up to one third of the year) (Montanari, 1999).

Based on themedieval religious doctrines concerning a “spiritualgeography”, the burial locations of the individuals possibly affectedby leprosy suggest a socially stratified society. Severe pathologicalchanges are seen in skeletons in the outskirts of the cemeteries andnot in the parts located near the churches. Furthermore, previousstudies of skeletal medieval samples from the same site have showndifferences in dietary patterns, most likely based on social stratifi-cation. Surprisingly, a clear social dichotomy is not observed in thediet of the affected. Individuals with bone changes indicative ofsystemic diseases such as leprosy had the same diet as the (at leastseemingly) unaffected community at the same cemetery. On theother hand, the individuals buried in the same area as the sixpossible cases of leprosy could have been sick for a long time fromdiseases that do not affect the skeleton. Hence, comparisonsbetween skeletons with and without skeletal changes are notnecessarily the same as comparisons between unhealthy andhealthy individuals. However, leprosy affected could, according tohistorical sources, be seen as a group of their own, with a moresevere social stigma than others. It is possible that the sample isspatially biased, and that a different result would have beenobtained had individuals buried within the church building (clearlysignifyinghigher status) been included.With the results inmind, it istherefore suggested that if there existed a dietary differencebetween infected and seemingly healthy people it was not a differ-ence in food source but rather in other parameters, i.e. the same typeof food was consumed but in varying quality and freshness.

Both the archaeological and the rare historical records indicatethat different social groups in society used the churchyard at theHumlegården block and the one belonging to Church 1 (Kjellströmet al., 2005; Wikström, 2008). Comparing the sample from Humle-gården (Church 2) as a whole with a sample from a contemporarygroup of people buried in another churchyard (Church 1), somedifferences in carbon values were discernable. This shows that die-tary differences indeed existed in Sigtuna. The results suggest thatthe people in the Humlegården block consumed fewer vegetablesbut the same amount of freshwater fish as a contemporary group ofpeople from another cemetery. As in the previous study (Kjellströmet al., 2009), the difference could have socio-cultural or socio-economic explanations. Although a supposed social hierarchy isimplied by thediscoveryof the groupwith signs of systemic diseases(including both leprosy and tuberculosis) in the outskirts of thechurchyard, the differences cannot be verified through the dietaryanalysis. Instead, it seems like the borders of the churchyards notonly delimit the distribution of the graves but also symbolize socialrestrictions and differences in consumption. This is in accordancewith the generally high prevalence of pathological changes at theHumlegården block compared to other cemeteries (Kjellström andWikström, 2008). Furthermore, even though the six most afflictedindividuals did not differ in diet from the rest of the sample, it is notclear that they shared food of the same quality and freshness.

9. Conclusions

Knowledge of the diet during themedieval period ismainly basedon written sources. As an increasingly substantial archaeological

material is unearthed and analysed, it is becoming possible toexamine the diet in a more direct way. From the few comparableisotopic studies performed on medieval populations (Privat et al.,2002; Polet and Katzenberg, 2003; Bayliss et al., 2004; Müldner andRichards, 2007; Fornaciari, 2008), the results indicate a diet basedon terrestrial sourceswitha rather large inputof freshwaterfish. Ithasalso beenpossible to investigate potential differences in diet betweensocial groups and, as in this study, between healthy individuals andthose affected by systemic disease.

When analysing the sulphur isotope composition, no differencescould be ascertained in either affected versus non-affected groupsor females versus males. This would indicate that the people buriedat Humlegården originated from the same region or at least that noclear distinctions can be made between the origins of the twogroups. Comparing the animal reference d34S measurements withthe human d34S values, the origin of the people buried here seemsto be predominantly local but with a few exceptions. This all fitswith Sigtuna’s status as a town and trading centre with people fromaround the Baltic Sea.

The burial locations of the affected suggest a socially stratifiedsociety and social stratification has been indicated in previousstudies. No dietary differences were observed between affected andnon-affected individuals or between females andmales. Differenceswere only found when comparing the total sample with a contem-porary cemetery. Given that socially defined diets existed thesemayhave been expressed as differences in food quality rather than foodsource. The results from the present study highlight the hierarchicalarrangements of social classes in the early medieval society.

Acknowledgements

We would like to thank Sigtuna museum for access to the Sig-tuna skeletons. We would also like to thank the anonymousreviewer for the comments.

Grant sponsorship: Berit Wallenberg foundation.

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