New Light on Oblong Forts: Excavations at Dunnideer, Aberdeenshire
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Proc Soc Antiq Scot NEW140 (2010), LIGHT 79–91 ON OBLONG FORTS: EXCAVATIONS AT DUNNIDEER, ABERDEENSHIRE | 79 New light on oblong forts: excavations at Dunnideer, Aberdeenshire Murray Cook* with contributions by Hana Kdolska, Lindsay Dunbar, Rob Engl, Stefan Sagrott, Denise Druce and Gordon Cook ABSTRACT This paper presents the results of the excavation of a single keyhole trench at the oblong vitrified fort of Dunnideer, Aberdeenshire, along with a brief history of the study of oblong forts and vitrification. The excavation yielded two radiocarbon dates derived from destruction layers, which are discussed along with the results of a limited programme of archaeomagnetic dating at the same location. INTRODUCTION ramparts, it also has an entrance so may not be part of the oblong fort series. In addition, The series of oblong, gateless and often there has been significant debate over vitrified forts are one of the iconic type-sites of contradictory sets of dating evidence from the the Scottish Iron Age. Their study echoes the series (Alexander 2002). This article presents development of modern Scottish archaeology, the results and implications of the first new with its origins in the intellectual explosion excavation evidence for over 30 years. of the Scottish enlightenment; indeed, the earliest research (Williams 1777) just predates the founding of the Society of Antiquaries ARCHAEOLOGICAL BACKGROUND of Scotland in 1781. However, despite over 200 years of study, their function and date The forts in question are rectangular, with remain uncertain. This is largely because only massive stone timber-laced ramparts, two examples have been subject to modern frequently vitrified, without obvious excavation: Finavon, Tayside (MacKie 1969a entrances, often on prominent hilltops, and and 1976) and Craig Phadrig, Inverness ranging widely in area by a factor of 10 from (Small & Cottam 1972). Another potential c 0.06 ha to c 0.8 ha (Feacham 1966: 67, fig example is Greencairn, Balbegno, Fettercairn 5). While the series is most commonly found whose excavation yielded radiocarbon dates in the north-east of Scotland (Tayside and associated with destruction across the second Aberdeenshire) it has been argued that outliers half of the 1st millennium bc (Wedderburn exist across the rest of the country (for example 1973). However, while it has massive vitrified Dunagoil, Isle of Bute (Harding 2004), * Oxford Archaeology North, Mill 3, Moor Lane Mills, Moor Lane, Lancaster LA1 1GF 80 | SOCIETY OF ANTIQUARIES OF SCOTLAND, 2010 although this is questioned by others (Fraser the air of impregnable fortresses, alternative Hunter pers comm). The series includes both interpretations have been voiced, such as non- the second highest hillfort in Scotland, Tap defensive ceremonial structures, with parallels o’Noth, at 563m OD (RCAHMS 2007: 103–5) to European ritual enclosures (Harding 2004a: and reputedly the fort with the highest density 87). Their chronology has been subject to of finds in Scotland, Dunagoil (Dunwell & considerable debate; for example, while Armit Ralston 2008: 83). (1997: 108) and Ralston (2006: 151) prefer The initial studies of the series started in to see the series as belonging to the latter the late 18th century with a clear focus on centuries bc, Halliday (1991) and (Ritchie their vitrification (Williams 1777; Anderson 1995, 8) have argued for Pictish dates. 1779, 1782; Tytler 1790). Research faltered, The importance and wide interest in the then restarted with the Victorian excavations forts has led to various techniques being at Castle Law, Abernethy and Castle Law, applied to date the forts, from radiocarbon Forgandenny, both Perth and Kinross, which dating of charcoal connected with the revealed timber lacing (Christison & Anderson destroyed rampart (Mackie 1969 and 1976; 1899; Bell 1893). These excavations provided Small & Cottam 1972; Wedderburn 1973) to the inspiration for Childe’s Abernethy dating the actual vitrification event by both Complex (1935: 193–7), assumed to have been thermoluminesence (TL) (Sanderson et al derived from the murus gallicus described by 1988) and archaeomagnetism (AM) (Gentles Caesar at Avaricum (Cotton 1954), helping to 1993). The former dates could relate to the provide a lynchpin for diffusionist theories use of the sites and represent termini post of cultural change through invasion (Harding quem for the construction of the ramparts, 2004a: 85). It was only with the eventual while the latter clearly relate to their introduction of radiocarbon dates that the destruction and represent termini ante quem origin of the forts was pushed back (Mackie for the use of the site. However, these various 1969b), making such theories untenable. methods give inconsistent dates, ranging Childe also drew a distinction between those from 1000 bc to ad 1000 (Sanderson et al of the series that were vitrified and those 1988: 315; Ralston 2006: 150–1; RCAHMS that were not (ibid), with his excavations at 2007: 102). Finavon characterising the former (Childe Mackie’s dates are considered problematic 1935a). This excavation provided the starting due to laboratory problems, and are currently point for Childe and Thornycroft’s (1938) only recommended for use with so large an experiments into vitrification. error range that they simply indicate activity in The forts continued to be an intermittent the 1st millennium bc (Alexander 2002: 51–3). focus of research through the 1960s (see Small and Cottam’s dates from Craig Phadrig below) to the present day, with detailed indicate that the inner vitrified rampart was surveys of the White Catherthun, Angus possibly constructed and then destroyed in the (Dunwell & Strachan 2007) and the ongoing second half of the 1st millennium bc (Small re-survey of Castle Law, Forgandenny (John & Cottam 1972: 23), although the material Sherriff pers comm) as well as a general call dated and its interpretation are not without for more excavation on them (Hunter 2007: controversy (Ralston 2004: 23). Finally, 49). there is some confusion over Wedderburn’s While the massive walls of these forts and dates from Balbegno, two of which are the apparent absence of entrances lends them statistically different, one from the middle of NEW LIGHT ON OBLONG FORTS: EXCAVATIONS AT DUNNIDEER, ABERDEENSHIRE | 81 the 1st millennium bc and the second from ‘homesteads’ are also the subject of debate the closing centuries bc (Megaw & Simpson (Taylor 1990). Some have Late Iron Age 1979: 489). The first date relates to a timber origins with frequent Early Historic reuse associated with the destruction of the wall, (Hingley et al 1997), but there is clear while the latter is associated with twigs under evidence that their number contains de novo the wall’s collapse. If the dates are accurate, it constructions from the Early Historic period may be that the older date represents residual (for example, Maiden Castle, Aberdeenshire material on site used as fuel to destroy the (Cook in press)). rampart or alternatively, perhaps it represents It is clear that the massive ramparts the difference in age between construction and represent a substantial investment of destruction, with the older date deriving from resources (timber and stone) as well as labour timber lacing. and effort. The subsequent vitrification, a While Sanderson’s TL dates were process by which stones are fused together at among the first attempts to date the actual temperatures in excess of 1,000°C (Ralston vitrification and represent important ground- 2006: 146), at some sites represents an even breaking works, the results were surprisingly more impressive process (see McHardy varied and they have come under increased (1906), Childe & Thornycroft (1938) and criticism (Kresten et al 2003; Ralston 2006: Ralston (1986)). Vitrification requires timber- 151). However, Gentles’ AM evidence on the laced ramparts and involves substantial four oblong forts he considered (Tap o’Noth, quantities of fuel over an extended period of Finavon, Knockfarril and Craig Phadrig) are time; it is argued that to achieve the level of generally consistent and indicated that the vitrification present on these sites would take vitrification occurred in the closing centuries days if not weeks (Ralston 2006: 163). The bc (Ralston 2006: 151). With specific process has no chronological or geographical reference to Finavon, an average of seven significance, and occurs over a wide period samples gave a date at 95% confidence of across Europe (ibid 143–63). 180–90 bc (Gentles, quoted in Alexander The factors leading to vitrification have 2002: 53). been discussed in relation to accidental Other indirect dating evidence is fire, constructional factors (a deliberate act available from some of the series: at Castle undertaken to strengthen the rampart), and a Law, Abernethy, a La Tène Ic bronze fibula deliberate act of destruction (Mackie 1969b, was recovered from the site (Christison & 1976 and Ralston 2006). Accidental fires Anderson 1899: 32; Feacham 1963: 145; would be unlikely to have such sustained Hull & Hawkes 1987), although it cannot effects and the unpredictability of the process be linked to the ramparts. At Castle Law, suggests it was not constructional. Current Forgandenny, new survey has revealed as views tend to see it as the latter, as an act of yet undated roundhouse platforms on the aggression following capture (Ralston 2006: collapse of the rampart (John Sherriff pers 163). However, if – as Harding (2004: 85–7) comm). In addition, there are no Roman suggests – the enclosures