Friday, November 1, 2013

The Knockgraffon Late Bronze Age House in its Radiocarbon Landscape

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The Knockgraffon Late Bronze Age House. JG O'Donoghue. Reproduced by permission.

Over the last while I’ve become a big fan of the art of JG O’Donoghue, the Cork-based artist and illustrator. He specialises in archaeological and heritage themes, but he’s also available for commission and sells his work via an on-line shop [Facebook | Website | Storenvy]. If all this wasn’t enough, he also runs a blog: Líníocht Blog. In a recent post on his Facebook page, he examined a possible Middle Bronze Age byre at Knockgraffon, Co. Tipperary and produced a reconstruction that was both a beautiful image and directly based on the archaeological evidence. He has now followed this up with a blog post of another exquisite reconstruction, again based on the archaeological evidence, of a Late Bronze Age house from the same townland of Knockgraffon.

I have two points in dedicating this post to the Knockgraffon house. First, I’d like to introduce as many people as possible to the work of a talented artist, and all-round good guy, JG O’Donoghue. Please go take a look at this stuff. Maybe buy a couple of his cards … you could send them to me! The other point of today’s post is to examine the ‘Radiocarbon Landscape’ of the Knockgraffon house. I have coined the term as an alternative, and complimentary, intellectual strategy which departs from traditional research pathways, such as the examination of sites of similar morphology. Just because individual sites appear similar does not guarantee that they are of identical age – indeed, they may be separated by hundreds of years. I’m not claiming that such an approach is invalid, just that there are alternatives.

The Knockgraffon Middle Bronze Age Byre. JG O'Donoghue. Reproduced by permission.

Even though archaeology is no longer my primary source of income, I still maintain my personal research project: Irish Radiocarbon and Dendrochronological Dates [Facebook | Website]. My work in cataloguing radiocarbon determinations and dendrochronological dates from Irish excavations has, so far, amassed over 7000 data points. As you may know, the Catalogue (available as an MS Excel document) is freely downloadable (or available directly from me by email) to all interested researchers, from professional academics to the ‘ordinary’ person on the street. I have chosen to keep the data in a relatively ‘ordinary’ format of MS Excel, rather than trapping it in a custom-built database, as I have found that this allows more people to view, access, and manipulate the information than might otherwise be possible. One of my key goals is to provide the maximum volume of data in the most ‘vanilla’ format possible, allowing individual researchers to tailor it to their own needs with the minimum of effort.

Plan of Knockgraffon Late Bronze Age House (McQuade, Molloy & Moriarty 2009, 76)

First of all, let’s examine the Knockgraffon house itself. The excavation was directed by Colm Moriarty, who runs [Facebook | Website | Shop] and published in the NRA volume In the Shadow of the Galtees (McQuade, Molloy & Moriarty 2009). The house survived as a curving set of seven post-holes on the southern side, with a further post-hole on the northern side. Two large post-holes are interpreted as internal roof-supports, while the entrance was defined by a set of post-holes that would have formed a porch structure. Taken together, the whole is interpreted as having constituted a round house, some 6m in diameter. Other than the roof supports, there were a series of internal features, including four pits, the majority of which were sub-circular with concave profiles. Outside the house, a sub-rectangular setting of four post-holes is interpreted as the supports for a raised granary. A further sequence of three post-holes, to the south of the house, is thought to be the remains of vertical supports for a fence or windbreak.

Radiocarbon dates contemporary with the Knockgraffon house. Click for larger image.

In terms of chronology, the activity at the site is dated by a single determination on pomaceous wood charcoal from one of the post-holes that made up the entrance porch (F87). The determination that came back from the laboratory was 2810±50 BP (Beta-220337). For anyone not familiar with the process of radiocarbon dating, this means that – judging by the rate of decay of the radioactive carbon isotope 14C – the wood died 2810 radiocarbon years before the present. First of all, ‘Present’ was established as 1950 AD as an unchanging point to be ‘before’. Also, radiocarbon years are not the same length as calendar years, which is why the date needs to be calibrated, to return it to a meaningful time-frame  There is also a standard deviation, or degree of uncertainty, attached to this figure, in this case 50 radiocarbon years. For anyone interested in more detail, I did a lecture to the NRA on this topic, that’s available as a PDF: here, and the final publication is available here. Once the determination has been calibrated into calendar years, we can see that the range (at 2σ, or 97%, level) spans the period from 1114 to 839 cal BC. Personally, I would have preferred to have seen a number of dates from this site. A single date is great, but it doesn’t allow us to draw out the potential for longer, phased activity on the site. However, in the context of a large road-development excavation like this, I’m just grateful that this one little house site has any date at all. But just what do we have? We can tell that the wood for the front-left post of the porch was cut down in the period from 1114 to 839 cal BC … we can say that this falls into the period that we call the Late Bronze Age (see Chapple 2008). Traditional research pathways include examining the morphology of the structure in relation to other known houses of similar date, and comparing and contrasting between similar structures from the same road scheme excavations. The overall authors of the monograph (McQuade, Molloy, & Moriarty 2009) do this in good style, and I in no way wish to detract from their achievement. The explosion of published, well-dated, excavations undertaken in the last decade or so is now sufficient that we can introduce another, complimentary, research path that can operate on the scale of a single decade. Interrogating the data in the IR&DD catalogue for just five radiocarbon years on either side of the central date (i.e. from 2805 to 2815BP) brings back 29 radiocarbon dates, representing 15 Irish counties (plus two from Iceland), and 26 individual excavations. Think about it! That’s just ten years … all other things being equal, the people who created these sites lived and died in the same narrow timeframe. The likelihood is that they shared a common language, and – even if only in the broadest sense – they shared numerous cultural connections. They were part of the same trade networks; they shared building traditions and burial traditions. Actually, as much as I’d like it to appear so, it’s not that simple. At the 2σ level, the standard deviations of these dates covers the period from 1294 cal BC to 795 cal BC, a period of almost 500 years. At the 1σ level, where the confidence that the events being measured occurred within the specified timescale are closer to 65%, the period ranges from 1114 cal BC to 839 cal BC, a period of 275 years. There are several reasons for this temporal spread, including the inconsistencies of the calibration curve, and the large standard deviations associated with some of the older determinations. In the latter case, two of the dates from Rathgall, Co. Wicklow, have standard deviations of 105 and 110 years. Even when taking such difficulties into consideration, we are still left with a range of dates that are as close to contemporary with the events at the Knockgraffon house as you are going to find.

Even in a brief list of dates such as this, there are other excavated houses. At Townparks, Antrim Town, material from a lined pit at House C was dated to 2810±50 BP (1114-839 cal BC, GU-11495)(Ballin Smith 2003, 41). At Carrigillihy, Co. Cork, a date of 2810±50 BP (1114-839 cal BC, GrN-12917) was returned from charcoal from the habitation layer of the later house (O'Kelly 1989, 348). Cherry (Prunus avium) charcoal from the slot-trench (F14) of the round house at Ballylegan, site 207.1, Co. Tipperary, dated to 2805±33 BP (1047-849 cal BC, UB-7214)(Stanley, Danaher & Eogan 2009, 169; McQuade, Molloy & Moriarty 2009, 366). At Clonadacasey 2, Co. Laois, a date of 2805±35 BP (1049-846 cal BC, SUERC-18510) was returned from charcoal (Pomoideae and ash) from a post-hole in Structure 2 (NRA Database). At Rathgall, Co. Wicklow, charcoal from Hearth 1 dated to 2810±105 BP (1288-796 cal BC, D-134)(Raftery 2004, 87). On the same site, charcoal from a pit at the south-west corner of Hearth 2, returned a date of 2810±110 BP (1294-795 cal BC, D-133)(Dresser 1980, 1028).

This is the Bronze Age, after all, so you should expect lots of burnt mounds. Oak, alder, hazel & Pomoideae charcoal from the fill of a stake-hole at Mullenmadoge II, Co. Mayo, dated to 2815±50 BP (1116-843 cal BC, GrN-30850)(Gillespie & Kerrigan 2010, 368). Charcoal from Trough 5 at Demesne or Mearsparkfarm 5, Co. Westmeath, dated to 2812±23 BP (1018-904 cal BC, UBA-8187)(NRA Database). A date of 2811±26 BP (1038-901 cal BC, UB-11275) was returned from hazel charcoal from fill of well/spring (C10) associated with the burnt mound at Caherweelder 1, Co. Galway (O'Mahony & Delaney 2010, 19; Delaney & Tierney 2011, 202-203). At Oldtown 1, Co. Laois, alder and hazel charcoal from a burnt mound trough dated to 2810±35 BP (1053-846 cal BC, SUERC-17992)(NRA Database). Charcoal from Parksgrove 2, Co. Kilkenny, dated to 2810±40 BP (1109-842 cal BC, GrN-25789)(Pers. Comm. R. Warner). At Kennastown 1, Co. Meath, a hazelnut shell from the fill of pit (C125, F127) was dated to 2810±40 BP (1109-842 cal BC, Beta-247079)(M3 Radiocarbon Date list). Hazel charcoal from the fill (C12) of a pit (C15) returned a date of 2809±20 BP (1010-909 cal BC, UB-11508) at Moyveela 2, Co. Galway (Mullins & Delaney 2010, 18; Delaney & Tierney 2011, 204-205). At Lisheen, Co. Clare, a date of 2808±33 BP (1050-849 cal BC, UB-6062) was returned from material recovered from a low mound of burnt stone overlying troughs (Grogan 2007, 210). Alder charcoal from a bedding layer (C617) of timber, associated with a working platform at the burnt mound at Caheraphuca 6, Co. Clare, dated to 2806±24 BP (1016-900 cal BC, UBA-12721)(Bayley 2010, iii, 9, 33).

In terms of contemporary burial, material from one of the cremation pits at Blackrath, Co. Kildare, returned a date of 2815±50 BP (1116-843 cal BC, SUERC-25366)(INSTAR Database). Human bone from a cremation burial in a coarse wear vessel at Rathgall, Co. Wicklow, dated to 2805±35 BP (1049-846 cal BC, GrA-22304)(Pers. Comm. R. Warner). Charcoal from a secondary feature inside the ring ditch at Ballyveelish 3, Co. Tipperary, returned a determination of 2810±90 BP (1253-806 cal BC, GrN-11656)(Lanting 1987, 29; Doody, 1987, 13). At Ballintaggart, Co. Down, charcoal from the central cremation (C131, F200) of ring ditch 5 (Area 2) returned a date of 2810±70 BP (1192-814 cal BC, Beta-217352)(Chapple, Dunlop, Gilmore & Heaney 2009, 76; Chapple 2008, 166; Chapple & Heaney 2010). Finally, at Carnkenny, Co. Tyrone, charcoal from the old ground surface sealed below the ring cairn returned a date of 2815±50 BP (1116-843 cal BC, UB-599)(Lynn 1973-1974, 30; Smith, Pearson & Pilcher 1973, 215).

There is only one shell midden in this group, at False Bay, Co. Galway, which dated to 2810±75 BP (1193-812 cal BC, KI-2899)(McCormick, Gibbons, McCormac, & Moore 1996, 83). There are three trackways from this period within the sample group. At Dromard More (Track B), Co. Tipperary, a piece of alder with bark, used as a runner on the trackway, dated to 2810±25 BP (1026-900 cal BC, GrN-18764)(Brindley & Lanting 1998, 55). An oak plank from the trackway at Baunaghra (Templetuohy Bog), Co. Laois, returned a date of 2805±45 BP (1111-836 cal BC, GrN-14732)(Brindley & Lanting 1998, 48). Finally, Track 3 at Derryoghil, Co. Longford, was dated to 2805±20 BP (1007-907 cal BC, GrN-15487)(Brindley & Lanting 1998, 51). The increased frequency of trackways from the Middle Bronze Age onwards is occasionally seen as a response to deteriorating climatic conditions (Grogan 2004). In this context it is particularly interesting that two dates in this sequence are related to the volcanic eruption of Hekla 3 in Iceland, which may well have had a significant impact on local conditions. The two dates are: 2810±80 BP (1208-810 cal BC, GU-7031) and 2810±50 BP (1114-839 cal BC, GU-7039)(Plunkett 2006, 62).

Other sites of similar date include Rath, Co. Meath, where one feature (F380) was dated to 2812±31 BP (1052-858 cal BC, Wk-18206)   (Pers. Comm. J. Gaffrey, CRDS Ltd.). At Hallsfarm 1, Co. Westmeath, charcoal from a spread of material returned a date of 2813±45 BP (1113-844 cal BC, UBA-8205)(NRA Database)

Taken together, this small group of radiocarbon determinations allows us to see beyond the immediate physical landscape, and past an examination of parallel morphologies, into an island-wide panorama of contemporary sites. Through this approach we can see the wider scope of contemporary human action – not just the construction of other houses, but the disposal of the dead, reaction to climate change, the exploitation of food resources … and whatever they did with burnt mounds. As more and more radiocarbon dates are published – and eventually make their way into the IR&DD Catalogue – combined with a more nuanced approach to sample selection and advances in dating technology, the numbers of accurate and precise dates will grow. As a direct result of this, the more fine-grained and narrow-ranged the ‘Radiocarbon Landscapes’ we are able to produce will become. I do not claim that it is a research ‘silver bullet’ that does away with any other avenue of research. Far from it! This approach, if used well, can become another valuable implement in the archaeological research tool-box. It may lack the immediacy (and beauty) of O’Donoghue’s excellent images, but this too is attempting to reconstruct an image of the Knockgraffon and its place in the landscape. Together we can write bigger, more comprehensive, and (ultimately) more beautiful narratives of the past.

My most sincere thanks go to JG O’Donoghue, for allowing me to use his beautiful illustrations in this post; and also to Colm Moriarty for being such a good sport and offering encouragement throughout.

Moriarty gives the calibrated date for Beta-220337 as 1100-830 cal BC. This is slightly different to the calibrated range of 1114-839 cal BC that I’ve used here. The reason for this is that I used Calib 6.1.0, implementing the IntCal09 curve (Reimer et al. 2009), while McQuade et al. (2009, 370) used the IntCal98 curve for dates from Beta Analytic Inc., though it’s not stated which particular computer program (and version) they used.

As I’ve stated above, the IR&DD catalogue is available to anyone – for free – to do with as they please. If you want to try your hand at creating a Radiocarbon Landscape to complement your own excavation or research project, it’s simple for you to do so – and you have my blessing. If you need help, I’d be more than happy to give whatever advice I can - for free. However, if you’d like me to give it a shot for you, I’d be up for that, too – and my rates are pretty reasonable!

I've sung the praises of JG's online shop above, but I should also point out that Colm Moriarty's also has an on-line shop selling 'wonderful things' ... go check it out!: here. If you're not sure that it's for you - just buy either the leather wallet, or the Viking belt and have them sent on to me! :)

Ballin Smith, B. 2003 'The excavation of two Bronze Age roundhouses at Townparks, Antrim Town' Ulster Journal of Archaeology 62, 3rd Series, 16-44.

Bayley, D. 2010 N18 Gort to Crusheen Road Scheme. Caheraphuca 3-13. Burnt mounds and pits. Final report. Unpublished archive report. IAC Ltd.

Chapple, R. M., Dunlop, C., Gilmore, S. & Heaney, L. 2009 Archaeological investigations along the A1 dualling scheme, Loughbrickland to Beech Hill, Co. Down, N. Ireland (2005). Oxford.

Chapple, R. M. & Heaney, L. 2010 'Loughbrickland addendum' Archaeology Ireland 24.3, 48.

Doody, M. G. 1987 'Early Bronze Age burials, Ballyveelish 3, Co. Tipperary' in  Cleary, R. M., Hurley, M. F. & Twohig, E. A. (eds.) Archaeological excavations on the Cork - Dublin gas pipeline (1981 - 82), 10-21, Cork.

Dresser, P. Q. 1980 'Dublin radiocarbon dates III' Radiocarbon 22.4, 1028-1030.

Gillespie, R. F. & Kerrigan, A. 2010 Of Troughs and Tuyères: The archaeology of the N5 Charlestown Bypass. Dublin.

Grogan, E. 2004 ‘Middle Bronze Age burial traditions in Ireland’ in Roche, H., Grogan, E., Bradley, J., Coles, J. & Raftery, B. (Eds), From megaliths to metals: essays in honour of George Eogan, 61-71. Oxford.

Lanting, J. 1987 'Appendix III. The radiocarbon dates' in  Cleary, R. M., Hurley, M. F. & Twohig, E. A. (eds.) Archaeological excavations on the Cork - Dublin gas pipeline (1981 - 82), 29-30, Cork.

McCormick, F., Gibbons, M., McCormac, F. G. & Moore, J. 1996 'Bronze Age to Medieval coastal shellmiddens near Ballyconneely' The Journal of Irish Archaeology 7, 77-84.

Mullins, G. & Delaney, F. 2010 'Archaeological excavation report. E3884 - Moyveela 2, Co.Galway. Burnt mound' Eachtra Journal 8, 1-37.

O'Kelly, M. J. 1989 Early Ireland: an introduction to Irishprehistory. Cambridge.

O'Mahony, E. & Delaney, F. 2010 'Archaeological excavation report. E3880 - Caherweelder 1, Co.Galway. Burnt mound' Eachtra Journal 8, 1-35.

Plunkett, G. 2006 'Hekla 3, environmental downturn and Irish Late Bronze Age hillfort connections revisited' Emania: Bulletin of the Navan Research Group 20, 62-67.

Raftery, B. 2004 'Pit 119: Rathgall, Co. Wicklow' in Roche, H. Grogan, E., Bradley, J., Coles, J. & Raftery, B. (eds.) From megaliths to metal: essays in honour of George Eogan, 83-90. Oxford.

Reimer, P. J., Baillie, M. G. L., Bard, E., Bayliss, A., Beck, J. W., Blackwell, P. G., Bronk Ramsey, C., Buck, C. E., Burr, G. S., Edwards, R. L., Friedrich, M., Grootes, P. M., Guilderson, T. P., Hajas, I., Heaton, T. J., Hogg, A. G., Hughen, K. A., Kaiser, K. F., Kromer, B., McCormac, F. G., Manning, S. W., Reimer, R. W., Richards, D. A., Southon, J. R., Talamo, S., Turney, C. S. M., van der Pilcht, J. & Weyhenmeyer, C. E. 2009 'IntCal09 and Marine09 radiocarbon agecalibration curves, 0-50,000 years Cal BP' Radiocarbon 51.4, 1111-1150.

Smith, A. G., Pearson, G. W. & Pilcher, J. R. 1973 'Belfast radiocarbon dates V' Radiocarbon 15.1, 212-228.

Stanley, M., Danaher, E. & Eogan, J. 2009 'Appendix 1 - radiocarbon dates from excavated archaeological sites described in these proceedings' in Stanley, M., Danaher, E. & Eogan, J. (Eds.) Dining anddwelling: proceedings of a public seminar on archaeological discoveries onnational road schemes, August 2008, 165-171. Dublin.

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