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Strontium Isotope Analysis on Bones

Until just a few years ago, isotope analysis could not be used on cremated remains because the heat of the pyre damaged the tooth enamel and altered the isotope signatures beyond recognition. However, scientists have now established that strontium isotope ratios are preserved in some cremated bones, in particular the petrous portion which contains the inner ear. The isotope ratios in these bones are, mainly, fixed in childhood so they provide a similar signature to the one in teeth, although not quite as well defined.
© University of Reading and Colchester Museum

Until just a few years ago, isotope analysis could not be used on cremated remains because the heat of the pyre damaged the tooth enamel and altered the isotope signatures beyond recognition. However, scientists have now established that strontium isotope ratios are preserved in some cremated bones, in particular the petrous portion which contains the inner ear. The isotope ratios in these bones are, mainly, fixed in childhood so they provide a similar signature to the one in teeth, although not quite as well defined.

photo of the petrous portion against a ruler measuring approx.4mm

Figure 1: Petrous portion of the inner ear

Strontium Isotope Analysis of Roman Bones at Colchester

Our research team selected 22 cremations where the petrous bone survived for strontium isotope analysis. They were all from Roman cemeteries around Colchester, included a range of vessel types (from the rarely found lead vessels to the most common coarse ware pots) and covered the first to third centuries AD. After carefully preparing the samples to remove contaminants, the isotope ratios were analysed using a Mass Spectrometer.

Colchester is situated in a region of varied geology comprised of sands, gravels and London clay. In the graph (Fig. 2) the range of strontium isotope values expected from the different types of rock is shown as two black dotted lines (Sr between 0.7090 and 0.7110). It’s likely that most of the individuals who plot within that box were local, although isotope values in this range are not very diagnostic and they could also have come from one of the many regions of Britain and continental Europe that have a similar strontium isotope signatures.

scatter graph showing strontium isotope ratios (vertical axis) plotted against strontium concentration in parts per million (horizontal axis). Most data points lie in the ratio range 0.7090 and 0.7110 but 5 individuals fall outside this area: COL_5, COL_6, COL_8, COL_20 are above, COL_17 is below

Fig.2: Strontium isotope values from 22 Colchester cremations (Joanna Moore, Durham University). The horizontal axis shows strontium concentrations as parts per million and the vertical axis displays strontium isotope ratios. Click to expand.

Five individuals showed 87Sr/86Sr values inconsistent with a childhood spent in Colchester. Pinpointing their origins is, however, difficult. Individuals COL_5, COL_6, COL_8 and COL_20 have higher 87Sr/86Sr values indicating origins in regions with older rock types found in Britain further to the west and north, as well as in continental Europe. Individual COL_20 in particular could be from Wales or the southwest coast of England, but this individual could also have spent their early childhood in regions of western Germany or southern Belgium. Individual COL_17 has a lower 87Sr/86Sr value consistent with a childhood in an area dominated by chalk or certain limestones which also occur widely in Britain and continental Europe.

Strontium Isotope Analysis Limitations

Isotopic analysis on its own is not enough to paint a broader picture of Romano British individuals. It’s only by combining all the information we’ve discovered (grave goods, burial rites, isotopes) that we can deduce the more nuanced and interesting stories of the people of Roman Britain. What can we learn from the grave goods the 5 incomers were buried with? Of the five, three were buried in locally produced greyware pots (COL_5,COL_8 and COL_17), showing that some incomers adopted local forms of pottery and burial rites. One was found in a coarse ware facepot (COL_6) and one in a lead vessel (COL_20 which is the individual you’ve been following). The lead vessel and the fact that this individual’s grave was covered by a barrow suggests that COL_20 was a high-status figure in the Roman administration or perhaps a merchant.

© University of Reading and Colchester Museum
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Dead Interesting: Uncovering Roman Britain in Old Museum Collections

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