Accurately dating the past – OxCal: free software for the calibration of radiocarbon dates
Submitting InstitutionUniversity of Oxford
Unit of AssessmentGeography, Environmental Studies and Archaeology
Summary Impact TypeTechnological
Research Subject Area(s)
Mathematical Sciences: Statistics
Earth Sciences: Geology
History and Archaeology: Archaeology
Summary of the impact
OxCal is the most popular software package world-wide for calibrating and
analysing dates within the carbon dating process, enabling the accurate
dating of objects from the past. The brainchild of Prof. Christopher Bronk
Ramsey, Director of the Oxford Radiocarbon Accelerator Unit (ORAU), OxCal
is based on chronologies refined by the use of Bayesian statistical
methods, and provides users with access to high-quality calibration of
chronological data, now the basis for global chronologies. It is available
online and free to download, and has played a highly significant role in
establishing the ORAU as one of the pre-eminent international radiocarbon
dating facilities. Funded by the NERC, and used widely within professional
archaeology as well as other disciplines, OxCal has also played a key role
in research projects (within Oxford and beyond) brought to the attention
of the general public by the media.
OxCal was developed by Christopher Ramsey (Professor of Archaeological
Science) at the ORAU, to help with the application of Bayesian statistical
methods to the radiocarbon dating of archaeological material. Since then
it has been applied across a range of dating techniques including
Luminescence dating and Uranium series dating. By providing a method to
build coherent and accurate chronologies from a whole range of types of
scientific data, OxCal makes a significant contribution to both academia
and society's understanding of the past.
Building on statistical research by Cliff Litton and Caitlin Buck at the
Division of Statistics, Nottingham University, Ramsey developed OxCal as a
software tool which could be easily distributed to users world-wide, and
the first version of OxCal was presented in 1994 at the 15th
International Radiocarbon Conference, Glasgow, and freely distributed by
disc. Through the subsequent involvement of OxCal in other radiocarbon
dating projects, Ramsey developed the software to allow greater
flexibility in types of data that could be analysed, including more
complex stratigraphical relationships [Section 3: R1; R2]. In
2008, deposition models (environmental sequences relating to depth and
age) were developed and incorporated into the calibrations [R3].
Finally, in 2013, funded as part of the NERC RESET consortium grant
[see section 3], a new version (version 4.2) incorporated new types
of model suited to studying cultural developments by allowing for gradual
rather than abrupt change, and the ability to display chronological data
in a geographical context through mapping [R4].
The use of OxCal has also been central to the partnership between Oxford
University's Radiocarbon Acceleration Unit and that of the University of
Glasgow, East Kilbride. Together, they are funded by the NERC and the AHRC
as a national radiocarbon dating service which serves, on average,
around100 academics and 30 doctoral students per year. Ongoing
developments to OxCal have been widely disseminated by Ramsey through
keynote lectures, conference papers and talks within the UK, Europe, the
US, and Japan. Ramsey has presented more than 12 conference papers and
public lectures between 2008 and 2013, to archaeological and other
academic audiences (including the Geological Society). The research has
also been disseminated through frequent publication in peer-reviewed
journals such as Radiocarbon; these publications have a strong
presence in the citation indices.
OxCal is employed in a wide range of research projects, and has a direct
impact on the most fundamental of archaeological questions: date. For
example, it was used and further developed as part of the international
Egyptian Chronology Project (2006-2009), funded by the Leverhulme Trust [R7]
and led by Ramsey, to test the correspondence between historical
chronology and the radiocarbon dating of archaeological material. This
research produced findings which suggest that the New Kingdom started
between 1570 and 1544 B.C.E, earlier than previous historical estimates [R5].
These results were disseminated through publication, including the Science
magazine, and in an open conference held in 2010, and received significant
press attention. This work was the subject of a book published by OxBow in
2013 and has led to a follow-on Leverhulme-funded project looking at the
origins of the Egyptian state.
The development of OxCal has also been supported by the work of two
doctoral students at Oxford university, engaged in scientific dating
projects. Daniel Miles (2001-2005; now an honorary research associate and
Senior Partner at the Oxford Dendrochronology Laboratory) undertook, as
part of his thesis, the development of the OxCal software for use in
tree-ring dating; and Sharen Lee's NERC-funded DPhil (2008-2012), which
included work on statistical methods for OxCal in her study of human
responses to rapid environmental transitions, where she focussed on
methods to assess rates of change in the archaeological record.
References to the research
[R1] Bayliss, A., and Bronk Ramsey, C. 2004. Pragmatic Bayesians:
a decade of integrating radiocarbon dates into chronological models. In C.
E. Buck and A. R. Millard (eds), Constructing Chronologies: Crossing
Disciplinary Boundaries (Lecture Notes in Statistics 177), 25-41.
[R2] Bronk Ramsey, C. 2009. Bayesian analysis of radiocarbon
dates. Radiocarbon 51(1), 337-360.
[R3] Bronk Ramsey, C. 2008. Deposition models for chronological
records. Quaternary Science Reviews 27(1-2), 42-60.
[R4] Lee, S. and Bronk Ramsey, C. 2012. Development and
application of the trapezoidal models for archaeological chronologies. Radiocarbon,
NERC Consortium grant of £588,000 the Research Laboratory for Archaeology
and the History of Art (RLAHA) at Oxford's School of Archaeology at
Oxford, as part of the overall project RESET (`Response of Humans to
Abrupt Environmental Transitions'). 2008-2013. Within the RLAHA, C. Ramsey
is the Co-Investigator coordinating Topic WP-7: the project's data
synthesis and age modelling.
RESET project website: http://c14.arch.ox.ac.uk/reset/embed.php?File=index.html
RESET Topic WP-7 webpage: http://c14.arch.ox.ac.uk/reset/embed.php?File=WP7.html
Leverhulme Trust research grant (F/08 622/A) of £245k. 2006-2009. To
support development of methods for the Egyptian Chronology Project.
Principal Investigator: C. Ramsey.
OxCal website and programme:
OxCal website, with access to programme: http://c14.arch.ox.ac.uk/oxcal.html
Details of the impact
Oxcal's reach is broad thanks to the fact that it is free to download,
and to use online, and thus attracts a large number of users, including
professional organisations, research bodies, and archaeological
enthusiasts. In the last year (up to the end of the census period) there
were 5,343 active external users of OxCal who used the programme more than
once. The programme is accessed from outside the RLAHA about 35,000 times
a year, or about once every 15 minutes. Of these external users almost
half (2,416) are using the programme very regularly (on average just over
once per month, accounting for 86% of the total external usage). At the
time of writing there are 12,800 sites linking to OxCal with 4,600 direct
links to the programme. Through the Oxford-East Kilbride Partnership,
OxCal is also used as part of the dating services offered to both the
academic community and non-academic users. It also features in the
curricula of a number of UK and overseas HEI scientific archaeology
courses, which has significantly contributed to the training of both
academic and non-academic users in the use of this software and dating
techniques, and features on a number of HEI courses beyond the UK, for
example Harvard's Anthropology course [Section 5: C7].
OxCal's impact on archaeological dating beyond academia is particularly
significant for two major groups of users:
1. Professional organisations:
Of the wide array of professional users, three examples are given here to
show the breadth and depth of the impact of OxCal on the commercial
sector, both in the UK and abroad.
a) English Heritage (EH) uses OxCal for calibrating all dates
produced in their date lists [C1, C2]; they recommend the use of
OxCal to commercial archaeological units; and have funded numerous
projects in which OxCal has been used. One such recent project, `Gathering
Time', published in 2011, was a major radiocarbon dating programme jointly
funded by EH and the AHRC, comprising the largest application of the
Bayesian approach to modelling archaeological chronologies ever
undertaken. The use of the Bayesian chronological model to interpret the
radiocarbon dates was pivotal to the success of the project, providing
more precise timescales for monument construction than had previously been
possible [C3]. All the chronological modelling was undertaken using
the programme OxCal version 3.10; as noted in the publication, `Without
this type of user-friendly software and modular model construction, an
application on this scale would simply not have been possible' [C3,
reference 3, p.58]. The results revised our picture of Early
Neolithic Britain and Ireland, establishing that the main period of
construction of causewayed enclosures was much briefer than previously
assumed, and revealing concentrated episodes of construction. In 2006, the
format of OxCal was changed so that it could be accessed online and thus
be compatible with all computer systems (version 4.0); these developments
were funded by a grant of £20k from English Heritage as part of their
Historic Environment Enabling programme.
b) The United States Geological Survey, a scientific agency of
the US government, uses OxCal as a tool for constructing chronologies [C4;
C5]. Specifically, OxCal is used to analyse recurrence rates of
environmental hazards such as earthquakes from the geological record,
which provide a critical constraint in estimating the seismic hazards
posed by active faults. These data are then used to calculate the risks of
further events [C5]. This is made possible by the model's
incorporation of all chronological constraints (including stratigraphic
order, the timing of the most recent event, and historical constraints),
which is freely available to paleoseismologists as part of the current
c) The Oxford Dendrochronology Laboratory (ODL) is a commercial
tree-ring laboratory set up by Ramsey's former doctoral student and OxCal
specialist, Dr Daniel Miles. Using OxCal as part of their methods, Miles
and his colleague Martin Bridge (as the Senior Partners) provide dating
services for private projects, as well as for EH, the Historic Royal
Palaces Agency and various professional archaeology units. Between 2008
and 2013, 20 timber buildings (including churches, domestic structures and
one hospital) across England have had the felling date ranges made much
more precise through the application of the OxCal tool, in some instances
having a significant effect on the interpretation of the buildings being
studied. The Brethren's Hall at St Cross Hospital, Winchester, for
example, had its felling date range reduced from 28 years to 14, allowing
the builder to be identified as Cardinal Henry Beaufort [C6].
2. The general public:
By making OxCal free, Ramsey has made the software available to all those
who wish to use it. Individuals with a particular interest are supported
by a dedicated OxCal e-mail list, and by an online discussion group used
by academics and non-academics across the globe [C8].
OxCal has also had an impact on the wider public by underpinning various
research projects of significant public interest which have received broad
media coverage. Three examples are given here, in which the extra
precision that OxCal has made possible has led to significant improvements
in dating, sufficient to have captured the public's imagination:
a) The bones excavated under Greyfriars Church in Leicester, in
2012, and subsequently identified as belonging to Richard III have
attracted a great deal of public interest; the radiocarbon dating of the
bones, which used the OxCal programme, was critical to this analysis and
identification, as reported in the BBC news and a Channel 4 documentary [C9].
b) The radiocarbon dating of David Attenborough's Madagascan
`elephant bird' egg, carried out by the Oxford Radiocarbon
Accelerator Unit, also used the OxCal tool; the result was broadcast in a
BBC documentary in 2011 [C10], where the egg was shown to belong
towards the end of a series of dates for this avian species previously
gathered by the ORAU, and it was shown that the bird had co-existed with
human occupants of Madagascar for some time before its extinction by the
end of the 1st millennium AD.
c) The findings of the Egyptian Chronology Project, discussed
above, also received significant press attention within the UK in 2010, in
national press (e.g. the BBC and Daily Mail), on popular archaeology sites
(e.g. AboutArchaeology.com), and in popular science publications (e.g. Nature
and Science) [C11].
Sources to corroborate the impact
[C1] Letter of support from the Head of Strategic Planning and
Management Division, English Heritage, confirming the importance of the
OxCal calibration software for the archaeological profession in England.
[C2] Bayliss, A., Bronk Ramsey, C., Cook, G., van der Plicht, J.
and McCormac, G. 2008. Radiocarbon Dates: From Samples funded by
English Heritage under the Aggregates Levy Sustainability Fund 2004-7.
Available at http://www.english-heritage.org.uk/publications/radiocarbon-dates-alsf-2004-7/
[C3] Whittle, A., Healy, F. and Bayliss, A. (eds) 2011. Gathering
Time: Dating the Early Neolithic Enclosures of Southern Britain and
Ireland. Oxford: Oxbow Books.
[C4] Sample tutorial file for calculating ages of paleoearthquakes
using Oxcal software, provided on the US Geological Survey's website:
[C5] Lienkaemper, J. J. and Bronk Ramsey, C. 2009. OxCal:
Versatile tool for developing paleoearthquake chronologies — A primer. Seismological
Research Letters 80(3), 431-434.
[C6] The Senior Partner at the Oxford Dendrochronology Laboratory
[C7] Syllabus of Harvard University's Anthropology course 2250A
(2011), as one example of OxCal's impact on students and teaching which
extends significantly beyond Oxford University:
Individual users and the general public:
[C8] OxCal Users Discussion Group online, demonstrating the range
of non-academic and international users of OxCal: https://groups.google.com/group/oxcal/topics?hl=en
[C9] Dating of bones of Richard III (`Richard III: The King in the
Car Park', Channel 4 documentary, Feb 2013): http://www.channel4.com/programmes/richard-iii-the-king-in-the-car-park/4od#3479296
[C10] David Attenborough documentary on the `elephant bird' egg
(`Attenborough and the Giant Egg', BBC documentary, March 2011): http://www.bbc.co.uk/programmes/b00z6dsg;
[C11] Egyptian Chronology Project: reports by BBC,
AboutArchaeology.com, The Daily Mail, Nature and Science: Links available