Published by Maney Publishing (c) The Vernacular Architecture Group Vernacular Architecture, Vol. 38 (2007) 87–97 ‘REV THOMAS BAYES: GET READY TO WIGGLE’ — BAYESIAN MODELLING, RADIOCARBON WIGGLE- MATCHING, AND THE NORTH WING OF BAGULEY HALL W. Derek Hamilton, Alex Bayliss, Adam Menuge, Christopher Bronk Ramsey, and Gordon Cook The principles of the Bayesian approach for modelling chronologies has been outlined in Bayliss (this volume). This paper applies these methods to a ‘real world’ problem of dating a phase of construction where the potential for tree- ring dating is limited. The accuracy and precision that these new techniques can deliver is demonstrated. Bayesian modelling of radiocarbon dates and tree-ring dating independently estimate construction of the north wing in the third quarter of the fifteenth century. © 2007 The Vernacular Architecture Group DOI: 10.1179/174962907X248083 INTRODUCTION Historically, the terms ‘radiocarbon dating’ and ‘buildings archaeology’ have seldom gone hand-in- hand due to lack of precision and high cost. The increased precision resulting from radiocarbon wiggle- matching of tree-ring sequences that cannot be abso- lutely dated through dendrochronology is not new (e.g., Clarke and Renfrew 1972; Clarke and Morgan 1983; Baillie 1995, 69–70), but until now it has been largely confined to assemblages of waterlogged wood (e.g., van der Plicht et al 1995; Bayliss and Pryor 2001; Kromer et al 2001; Bayliss et al 2003). This is because large samples of wood were required for conventional high-precision radiocarbon dating, which are seldom available from a standing building unless large pieces of timber are being replaced. Recent advances in the accuracy and precision of radiocarbon measurements produced by Accelerator Mass Spectrometry (e.g. Bronk Ramsey et al 2004; Dellinger et al 2004), however, now make radiocarbon dating of sufficient precision and accuracy for wiggle- matching to be feasible for small wood samples, such as those available from cores taken for tree-ring dating. An excellent summary of the history and variety of approaches employed for wiggle-matching is provided by Galimberti et al (2004). Arnold et al (2006) and Bayliss et al (2006) have clearly shown the precision that wiggle-matching can provide for dating a single core and a site tree-ring sequence, respectively, in the medieval period. This approach is wonderful for those cases where the den- drochronological samples cross-match and form a floating undated chronology — but what of sites where the timbers simply have too few rings available for reliable tree-ring analysis, and if we can produce 14 C dating for these timbers how can we combine this with our understanding of the construction history of a timber building? We believe the Bayesian approach to chronological modelling is ideal for these situations (see Bayliss, this issue), and we present here a case study where it is used to provide an estimate for the felling of timbers used in the construction of the north wing at Baguley Hall, Greater Manchester. BAGULEY HALL Baguley Hall, Greater Manchester (NGR SJ 8162 8874) comprises a three-bay hall range with cross- wings to north and south and a two-storey porch (Fig. 1), and has been the subject of considerable architectural and archaeological research (Smith and Stell 1960; Keen 1976; Dixon et al 1989; Menuge and Taylor forthcoming). 1 At the heart of Baguley Hall stands a hall range, built from massive timbers on the site of an earlier aisled hall, known from excavation. The walls of the present hall are of an unusually elongated cross- section, described by some commentators as ‘plank construction’. A spere truss separates a cross passage from the rest of the hall, which survives as two bays divided by an open truss. The timber-framed north wall of the hall survives but the south end is formed by the brick wall of the wing. An extensive programme of dendrochronology has now been undertaken on the hall range. Eight samples