|Map of the British Isles, showing drinking-water oxygen isotope values and the 16 British archaeological sites (including three in York) with evidence for pre-modern people whose results are consistent with an early life spent in North Africa (image: C. R. Green, using a base-map image © BGS/NERC, reproduced under their non-commercial licence, as detailed on the BGS website).|
|Proportion of investigated sites from each period with at least one oxygen isotope result consistent with an origin in North Africa (image: C. R. Green).|
The rationale for using oxygen isotope evidence as a tool for identifying people from Africa in pre-modern Britain was set out at some length in a previous post—essentially, tooth enamel oxygen isotope values reflect those of the water that was drunk by an individual in childhood, with drinking-water values varying markedly with climate and related factors. As such, it should be possible to identify first-generation migrants to Britain in the archaeological record by measuring their tooth enamel oxygen isotope levels, so long as they grew up in a region with significantly different drinking-water values to those found in Britain, a criteria North Africa fits comfortably, with many parts of it possessing levels notably higher than those found anywhere in Britain or, indeed, Europe.
In order to make a first pass at trying to assess whether isotopic data can help answer the question of the potential number of African people in medieval and earlier Britain and the variations in this number over time, I pulled together a rough corpus of 909 oxygen isotopes results taken from individuals buried at 79 Bronze Age–Medieval sites across Britain published up to the start of 2016, and then sorted these into four broad chronological periods: Bronze Age–Iron Age (22 sites), Roman (15 sites), Early Medieval (29 sites) and Medieval (14 sites), with one site in use across two of the periods.(1) I then went through this material to identify individuals whose results are sufficiently elevated so as to be both clearly indicative of a non-local origin and most consistent with a childhood spent in North Africa, rather than anywhere in Britain or Europe.(2) Needless to say, taking such an overview of the entire period from the Bronze Age to the Medieval era via a single dataset produces some interesting results, as well as some pitfalls. The former can be summarized as follows:
- 20.3% of the 79 surveyed Bronze Age–Medieval sites contained at least one person who has results consistent with a childhood spent in Africa (n=16). As can be seen from the map included above, these sites are spread across Britain, with the majority coming from what is now England, although not exclusively so. Note, some of the 'gaps' in the resultant distribution may well be more apparent than real, stemming from a lack of published sites in some areas, such as north-western England and Norfolk.
- Sites possessing isotopic evidence consistent with the presence of first-generation immigrants from North Africa are found in all periods looked at, although there is a clear peak in the Roman era. The Roman era—the mid-first to early fifth centuries AD—has the greatest number of sites with such evidence, namely seven, these being Winchester (Lankhills), Gloucester, York (three sites: Trentholme Drive, The Railway & Driffield Terrace), Scorton near Catterick, and Wasperton. Furthermore, nearly 47% of all Roman sites where isotopic analysis has occurred have produced evidence suggestive of the presence of people who grew up in North Africa, a significantly higher proportion than is found for any other era. The next highest raw totals of sites with such isotopic evidence belong jointly to the 'Early Medieval' and 'Medieval' eras (four sites each), although it is important to note that the Early Medieval total results from over twice as many sites being isotopically investigated than is the case for the Medieval era—as such, whilst 28.6% of the Medieval-era sites in the corpus have isotopic evidence consistent with the presence of North African migrants, only 13.8% of the Early Medieval sites do. Finally, the Bronze Age–Iron Age is represented by only a single qualifying site on the Isle of Thanet, Kent, equivalent to 4.5% of all Bronze Age–Iron Age sites where isotopic analysis has taken place, although this Late Bronze Age–Middle Iron Age cemetery has multiple people with such results buried within it.
- In total, 3.7% of the 909 Bronze Age–Medieval individuals surveyed from these 79 sites have results consistent with a childhood spent in Africa (n=34). This percentage reflects the fact that the majority of the sites looked at here only contain one or two individuals with values high enough for inclusion in the present study.
- A small number of results are elevated to such a degree that they strongly indicate a childhood spent in the Nile Valley or Delta. Around 11.8% of the individual oxygen isotope results that were highlighted here were exceptionally elevated to above 21.0‰ δ¹⁸Op (n=4), a level that is probably indicative of a childhood spent in or around the Nile Valley, where equivalent values have been recorded from the ancient burial site at Mendes in the Nile Delta, Egypt, and other sites up to the third Nile cataract at Tombos. Interestingly, these results come from individuals spread across the chronological range: one from a Late Bronze Age burial at Thanet, Kent (ninth century BC); one from a Middle Iron Age grave at the same site (fourth century BC); one from Roman York (the Driffield Terrace site); and one from the medieval cemetery at Whithorn, Scotland (late twelfth to thirteenth century AD).
Of course, whilst the above isotopic evidence is certainly intriguing, there are undoubtedly pitfalls to be aware of. On the one hand, we need to be wary of overestimating the proportion of any North African migrants in pre-modern Britain using isotopic evidence. For example, sites are sometimes chosen for isotopic analysis because they look potentially 'interesting', as was arguably the case with the cemeteries at York, Winchester and Thanet, and such a situation might well lead to a greater proportion of positive 'hits' in any corpus aiming to look for potential evidence of long-distance migration. Similarly, it is not totally impossible that a few of the people with the more marginal results discussed here could just have had their origins in a small area of southernmost Iberia rather than North Africa, although the bar for inclusion in the present corpus was set at such a level as to hopefully significantly reduce the possibility of this, and a substantial proportion of the results included here are, moreover, well above any plausible southern Iberian range.(3) On the other hand, the corpus could well underestimate both the number of individuals who may have had their origins in North Africa and their chronological spread. So, for example, whilst over 900 results were surveyed here, we still end up with a situation whereby none of the individuals with elevated values date from the Late Saxon/Anglo-Scandinavian period (later ninth to eleventh centuries). Taking this as a reflection of a lack of people from Africa in Britain at that time would, however, be a mistake: not only do we have good textual evidence for the presence of such people in the British Isles, but there are three burials of people of African descent known from tenth- and eleventh-century Gloucestershire and East Anglia—the problem is simply that none of them have been subjected to isotopic analysis and so they haven't been included here. Likewise, there are at least four burials of people who appear to be of African descent in the medieval cemetery at Ipswich, but only one has been isotopically tested (interestingly, five of the post-medieval/sixteenth-century burials there also appear to be those of people of African descent). Finally, by adopting a fairly high bar to inclusion in the corpus so as to avoid—as much as possible—the risk of 'false positives', we actually end up excluding a significant number of individuals who are generally accepted as being of African origin. So, only three members of a group of thirteen burials from Lankhills (Winchester) have results high enough to be included in the current corpus, despite the fact that all thirteen are considered to form a sub-group that is probably of African origin within the cemetery. All told, therefore, it might well be wondered whether the above tendencies to both overestimate and underestimate don't, in fact, cancel each other out.
|North African unguentaria found in a grave from the Late Roman cemetery at Lankhills, Winchester, that is part of the sub-group with elevated oxygen isotope results mentioned above, but which has values just a little below the cut-off for inclusion in the corpus used in this post (image: Oxford Archaeology, reused under their CC BY-SA 3.0 license).|
1 This corpus is based primarily upon J. A. Evans, C. A. Chenery & J. Montgomery, 'A summary of strontium and oxygen isotope variation in archaeological human tooth enamel excavated from Britain', Journal of Analytical Atomic Spectrometry, 27 (2012), 754–64 and 'Supplementary Material I' (14 pp.), to which have been added studies published after that paper or missing from it, using a Google Scholar search to catch any publications that weren't already known. Note, the periods assigned to the results taken from Evans et al, 'Supplementary Material I', have been checked and revised by me for this corpus, as they were occasionally idiosyncratic: 'Roman' is here used as a catch-all term for results from the first to early fifth centuries AD, 'Early Medieval' for those results from the period between the early fifth and late eleventh centuries AD, and 'Medieval' for those from the twelfth through to the fifteenth centuries. The additional studies used in creating this corpus are as follows, arranged by date of publication: S. Lucy et al, 'The burial of a princess? The later seventh-century cemetery at Westﬁeld Farm, Ely', Antiquity, 89 (2009), 81–141; J. Montgomery, 'Isotope analysis of bone collagen and tooth enamel', in C. Lowe (ed.), The P.R. Ritchie Excavations at Whithorn Priory, 1957–67: Medieval Bishops' Graves and Other Discoveries (Edinburgh, 2010), pp. 65–82; A. M. Pollard et al, '"Sprouting like cockle amongst the wheat": The St Brice's Day Massacre and the isotopic analysis of human bones from St John's College, Oxford', Oxford Journal of Archaeology, 31 (2012), 83–102; S. E. Groves et al, 'Mobility histories of 7th–9th century AD people buried at early medieval Bamburgh, Northumberland, England', American Journal of Physical Anthropology, 151 (2013), 462–76; K. A. Hemer et al, 'Evidence of early medieval trade and migration between Wales and the Mediterranean Sea region', Journal of Archaeological Science, 40 (2013), 2352–59; M. Jay et al, 'British Iron Age burials of the Arras culture: a multi-isotope approach to investigating mobility levels and subsistence practices', World Archaeology, 45 (2013), 473–91; E. Kendall et al, 'Mobility, mortality, and the middle ages: identification of migrant individuals in a 14th century black death cemetery population', American Journal of Physical Anthropology, 150 (2013), 210–22; C. A. Roberts et al, 'Isotopic tracing of the impact of mobility on infectious disease: the origin of people with treponematosis buried in Hull, England, in the Late Medieval period', American Journal of Physical Anthropology, 150 (2013), 273–85; K. A. Hemer et al, 'No Man is an island: evidence of pre-Viking Age migration to the Isle of Man'. Journal of Archaeological Science, 52 (2014), 242–9; J. I. McKinley et al, Cliffs End Farm, Isle of Thanet, Kent. A Mortuary and Ritual Site of the Bronze Age, Iron Age and Anglo-Saxon Period with Evidence for Long-Distance Maritime Mobility (Salisbury, 2014); J. Montgomery et al, 'Finding Vikings with isotope analysis: the view from wet and windy islands', Journal of the North Atlantic, Special Volume 7 (2014), 54–70; H. Eckardt et al, 'The Late Roman field army in northern Britain? Mobility, material culture and multi-isotope analysis at Scorton (N. Yorks)', Britannia, 46 (2015), 191–223; S. A. Inskip et al, 'Osteological, biomolecular and geochemical examination of an early Anglo-Saxon case of lepromatous leprosy', PLoS ONE, 10.5 (2015), pp. 1–22, online at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0124282; R. Martiniano et al, 'Genomic signals of migration and continuity in Britain before the Anglo-Saxons', Nature Communications, 7 (2016), article 10326, 8 pp., online at http://www.nature.com/ncomms/2016/160119/ncomms10326/full/ncomms10326.html, and Supplementary Materials, 54 pp. (Table 3 and discussion in Supplementary Note 2). I also include 'Ipswich Man' in the corpus, a man of African descent who was buried in the thirteenth century in Ipswich, as he was isotopically investigated and consequently determined to probably have his origins in North Africa, although the results are still as yet unpublished: BBC, History Cold Case: Series 1, Episode 1—Ipswich Man (broadcast 27 July 2010); 'Medieval African found buried in England', Discovery News, 11 February 2013, online at http://news.discovery.com/history/medieval-african-england.htm; K. Wade, Ipswich Archive Summaries: Franciscan Way, IAS 5003 (2014), online at http://archaeologydataservice.ac.uk/archives/view/ipswich_5003_2015/downloads.cfm; and Xanthé Mallett, pers. comm..
2 The following footnote outlines the methodology adopted here. The conventional upper cut-off for phosphate oxygen isotope values for people who grew up in the British Isles is 18.6‰ δ¹⁸Op, although it has been suggested that people brought up on the far western margins of Britain and Ireland—where drinking-water oxygen isotope values are at their highest, between -5.0‰ and -4.5‰ δ¹⁸Odw (see map)—could theoretically have values up to 19.2‰ δ¹⁸Op (see K. A. Hemer et al, 'Evidence of early medieval trade and migration between Wales and the Mediterranean Sea region', Journal of Archaeological Science, 40 (2013), 2352–59; C. Chenery et al, 'Strontium and stable isotope evidence for diet and mobility in Roman Gloucester, UK', Journal of Archaeological Science, 37 (2010), 150–63; and especially J. A. Evans et al, 'A summary of strontium and oxygen isotope variation in archaeological human tooth enamel excavated from Britain', Journal of Analytical Atomic Spectrometry, 27 (2012), 754–64). As such, and in order to avoid as much doubt as possible, I decided only to look at people with tooth enamel phosphate oxygen isotope results of 19.2‰+ for this post. This reflects, across the entire resulting corpus, the childhood consumption of drinking-water with values from -3.5‰ δ¹⁸Odw up to +2.0‰ δ¹⁸Odw on the 2010 revised Levinson equation or -4.0‰ δ¹⁸Odw to +0.3‰ δ¹⁸Odw on the 2008 Daux et al equation—needless to say, whichever equation is used, these values are notably higher than the maximum British drinking-water value of c. -4.5‰ δ¹⁸Odw (found only in a few spots in the far west of the Outer Hebrides and Cornwall), but in line with results from North Africa, whilst the highest of the recorded results in the corpus can only be matched in the Nile Valley, as was discussed in a previous post. Indeed, over 50% of the individuals studied in this post have results of at least 19.5‰ δ¹⁸Op, equivalent to a drinking-water value of -2.8‰ δ¹⁸Odw (-3.5‰ δ¹⁸Odw) or more, significantly above any credible British range and only really paralleled in some areas of North Africa. Moreover, it is worth noting from the map attached to this post that none of the individuals who are included in the study corpus were actually found in the areas with the highest drinking-water values in Britain, removing any lingering potential doubt as to their non-local origin. In fact, only a single individual of the 34 discussed here was found in an area with a local drinking-water value above -6.0‰ δ¹⁸Odw, whilst the vast majority (79%) come from areas where drinking water values are between -7.0‰ and -8.5‰. As such, not only do they largely come from areas where the theoretical maximum for tooth enamel phosphate oxygen isotope values is closer to c. 18.5‰, according to Evans et al (2012, p. 759), not 19.2‰, but their results actually reflect the childhood consumption of water with values at least 3.0‰ higher than the local level right up to potentially as much as 10.2‰ higher (at the Driffield Terrace, York, site)—in all cases, this is significantly above any plausible variations around the local range and is massively so in the case of many results. Finally, it is worth noting that the adoption of this relatively conservative approach may mean that the number of individuals of in Britain who grew up in North Africa is underestimated, rather than overestimated. For example, even a small drop of the bar to include all those with results of 19.0‰ δ¹⁸Op or above more more than doubles the number to be taken into the current corpus from our main source (the 2012 Evans et al corpus), and it is worth noting that many of the people with results at this level are indeed usually accepted as being probable migrants from North Africa, as are a significant number of people with slightly lower results too (see, for example, Evans et al, 'A summary of strontium and oxygen isotope variation', pp. 760–2; K. A. Hemer et al, 'Evidence of early medieval trade and migration between Wales and the Mediterranean Sea region'; and the discussion in a previous post, 'Some oxygen isotope evidence for long-distance migration to Britain from North Africa & southern Iberia, c.1100 BC–AD 800', 24 October 2015, blog post, online at http://www.caitlingreen.org/2015/10/oxygen-isotope-evidence.html). Nonetheless, it was felt worthwhile to set the bar higher in the present study in order to minimize as fully as possible the risk of false positives, and also to avoid as much as possible increasing the chance of some of the people studied here could have their origins in the one other area of Europe with very high drinking-water oxygen isotope values, southernmost Iberia, see note 3.
3 The map included in Evans et al, 'A summary of strontium and oxygen isotope variation', p. 761, indicates that the only part of Europe other than Britain with water oxygen isotope values above -5.0‰ is a small area of the south-eastern Iberian peninsula. L. J. Araguas-Araguas & M. F. Diaz Teijeiro, 'Isotope composition of precipitation and water vapour in the Iberian Peninsula', in IAEA, Isotopic composition of precipitation in the Mediterranean Basin in relation to air circulation patterns and climate (Vienna, 2005), pp. 173–90 at p. 178, state that values in this area range down to -4.3‰ δ¹⁸O, which is slightly enriched over the upper end of the British range (c. -4.5‰ δ¹⁸O); they also indicate that similar values above -5.0‰ δ¹⁸O are found in limited areas of the south-western coast of Iberia too, contrary to Evans et al, with groundwater results of c. 4.0‰ or even slightly higher reported from a very small zone around Cádiz (Araguas-Araguas & Diaz Teijeiro, fig. 3 at p. 180). In consequence, the bar for consideration in the present post was set relatively high to reduce the chance of including people from southernmost Iberia in the corpus—as was mentioned in note 2, above, only people with tooth enamel phosphate oxygen isotope results of 19.2‰+ were considered here, which on the 2010 revised Levinson equation (as used in K. A. Hemer et al, 'Evidence of early medieval trade and migration between Wales and the Mediterranean Sea region', Journal of Archaeological Science, 40 (2013), 2352–59, and other recent studies) equates to the consumption of drinking-water with values of -3.5‰ δ¹⁸O or above, with the majority of the results included here moreover reflecting the consumption of drinking-water with even higher values than this, ranging from -2.8‰ δ¹⁸O right up to +2.0‰ δ¹⁸O, well above the southern Iberian range.
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