iron age

2.6 Chronological Schemes

The Three-Age System was embraced in Scotland before England (Rowley-Conwy 2007 and see also the ScARF Neolithic Panel report). In the first synopsis of the Scottish Iron Age, Joseph Anderson (1883) insisted that this period should not be assigned absolute dates as he felt, understandably at the time, that prehistory could have no specific chronology. Since then, the term ‘Iron Age’ has been used in Scotland for a period beginning as late as the first century BC, a full four centuries after it was understood by Hawkes and Kendrick (1931) to begin in southern England on the basis of theories involving “iron-using, Celtic-speaking colonists” spreading slowly up-country (Piggott 1958, 75). This diffusionist perspective (together with its exaggerated time-lag), however, became unsustainable in the face of new evidence and Piggott (1966, 3) subsequently backdated the inception of iron-using to 550BC. Following the radiocarbon revolution (Renfrew 1973), later writers moved the date even earlier, to the seventh-eigth century BC (e.g. Harding 1974, 14; Ritchie and Ritchie 1981, 89). The Iron Age has in the past been understood to terminate with the Roman invasion of AD78 or in the third century AD or later if Piggott’s (1966, 3) scheme is followed. Despite problems discussed in more detail below, this is still used by some researchers (e.g. Armit 1997; Armit and Ralston 2003), sometimes in a modified form (e.g. Hingley 1992, in which the terminal date was set at AD200, in order to separate clearly the Picts as an early Medieval phenomenon).

However, a project by Needham et al. (1997), aiming to establish an independent chronology for British Bronze Age metalwork through a programme of radiocarbon dating of associated organic materials, has led to a revision of the dating of LBA metalwork assemblages. This includes the backdating of the end of Ewart Park metalwork from 700BC to c. 800BC, suggesting that the LBA-IA transition should also be backdated by about a century (Needham 2007; but cf O’Connor 2007). There is no good reason in the evidence to suggest a time-lag between the development of styles of metalwork in later prehistory in different areas of Britain. There is a danger, of course, that the dating of events in the Early Iron Age is propelled backwards as a result of the ‘plateau’ in the radiocarbon calibration curve, which begins at around 800BC. Such uncertainties can only be resolved through future work, and for now it would seem reasonable to use 800BC as a useful marker for the beginning of the Iron Age (though the question of the introduction of iron is another contentious one; there is some evidence for its use in Britain from the 10th century BC (Collard et al. 2006), but very little sign of its early use in Scotland. The use of Bayesian statistics to separate out the AMS dates that fall within the plateau  on the radiocarbon calibration curve is a highly promising avenue for further research.

Since the late 1970s/early 1980s, however, some archaeologists working in Scotland have adopted a chronological scheme known as the long Iron Age based on a Scandinavian model, breaking down perceived barriers between the Late Bronze Age, the Iron Age and the Early Historic period and taking incursions by the Norse, rather than the Roman army, as the terminus of the period (e.g. Chapman and Mytum 1983; Ralston 1980; Haselgrove et al. 2001, 3; Harding 2004; Haselgrove et al. 2001, 3). The long Iron Age therefore covers the first millennia BC and AD (as epitomised in the naming of the First Millennia Studies Group), and has been summarised by Parker Pearson and Sharples (1999) thus:

Table 1: Parker Pearson and Sharples’ suggestions for chronological divisions within the Long Iron Age
Label Chronological Span
Early Iron Age 700-100BC
Middle Iron Age 200BC-AD400
Late Iron Age AD 300-900

A somewhat looser definition of the Later Iron Age, “in the first millennium AD prior to the Norse settlement” (Armit 1990b) was adopted for the Scottish Archaeological Forum of 1988; as Armit (1990b, 1-2) explained “…no precise dates [were] given for this…the division [was] clearly an arbitrary one…”. Since then, the term Late/Later Iron Age has been used more precisely. Sharples and Parker Pearson (1999) define it variously as AD300-900 or AD400-800. Downes and Ritchie (2003) quote it as AD300-800. Most recently, Harding (2004, 3) has argued for a “‘long’ Iron Age, in which ‘early’ represents a span of time that in Southern Britain would cover the whole of the pre-Roman Iron Age, and ‘late’ is applied to the first millennium AD from around its second quarter”. The 250 years between these two brackets becomes the Roman Iron Age. Harding rejects the use of the term Middle Iron Age in a Scottish context, arguing that it constrains the occupation of brochs to “a limited span of two or three centuries around the turn of the millennium”. This perceived failing would seem to be no more than conventional depending upon a rigid classification of brochs as ‘middle Iron Age’.

The usefulness of the term ‘long Iron Age’ has become particularly apparent in the Western and Northern Isles (e.g. Armit 1990a; Downes and Ritchie 2003), where in the past cellular buildings have been described as ‘Pictish’, despite the evidence for local continuity in architectural tradition, the lack of written records and the geographical distance from the Pictish heartland. The greater chronological fluidity offered by the term allows the archaeologist to appreciate the evolution of architectural traditions and social development in the longue dureé and over wide, and environmental very distinct, areas. The use of this long Iron Age reflects a distinct movement of interest towards the study of the Northern and Western Isles over the past twenty years. In the south and east of Scotland, the Norse incursion can be no more a logical stopping point than the Roman invasion or the first historical mention of the Picts is in the Atlantic north and west. There is much to be said for the adoption of a chronological scheme that does not lay so much stress upon the significance of the dates of the earliest surviving written records, and the rather artificial divisions between later prehistoric, Roman and Early Historic periods which result from this.

It is clear from this discussion that there is no universally accepted chronological scheme for the Scottish Iron Age. Although it has been said that the traditionally defined Iron Age (quoted as 700BC to AD500) merges ‘imperceptibly’ into the Early Historic (Armit 1997c, 15), there is evidence for major changes in the settlement record of many areas from c. AD 400 if not from c. AD200.

5.2.2 Broad regional or national trends, versus local distinctiveness

National trends

Any discussion of Iron Age settlement and society needs to start in the Late Bronze Age (Harding 2006, 79). Roundhouses were being built across Britain from c. 1800 BC (Armit 2003, 33), and over time gave rise to a diverse range of regional forms. These Bronze Age origins are notably not the case in parts of Atlantic Scotland (e.g. the Northern Isles), where cellular forms remained the vernacular style. The Iron Age roundhouse, however, is not a straight continuation of a Bronze Age prototype (Harding 2009, 144-5) but represents a development of the concept during a period of significant change in roundhouse architecture circa 800-600BC (Pope 2003, 2007).

There is a great preponderance of round or oval buildings within the Early and Middle Iron Age settlement record across Scotland. There is, however, also a much smaller range of other structures present, of unrelated forms, that are generally ascribed a non-domestic function (i.e souterrains, 'four-posters' and a miscellany of odd structures like that at An Dunan, Uig, Western Isles (Gilmour 2002)); some are considered further below.

‘Substantial houses‘ (Hingley 1992, 1995) were a conspicuous feature across Scotland in the Early Iron Age irrespective of architectural detail, and continued to be common in Atlantic Scotland in the Middle Iron Age (complex Atlantic roundhouses, broch towers, wheelhouses). However, elsewhere in Scotland such substantial houses appear to become less frequent, though some do occur, in the early first millennium AD (e.g. the ‘southern brochs‘, Culhawk Hill (Rees 1998), big timber houses in the South-west, e.g. Rispain Camp (Haggarty and Haggarty 1983), and large ring-ditch houses in the Moray Firth area (e.g. Birnie and Culduthel).

Smaller Early Iron Age houses exist and have probably been under-researched as attention has tended to focus on the larger houses (Ralston and Ashmore 2007, 232).

In the Atlantic Late Iron Age there would appear to be an increasingly diverse range of structural forms. These are predominantly cellular forms, but there are also a small but significant proportion of rectilinear structures like the wags (stalled buildings) and similar structures (Baines 1999, Cowley 1999), some Argyll duns, and the external buildings at Dun Vulan (Parker Pearson et al. 1999) for example. Questions over the function of many of these buildings are yet to be satisfactorily resolved. There is also some continuing use of circular forms (e.g. wheelhouses at Scatness; Dockrill et al. 2010 and forthcoming).

But how significant is the difference? Should wags be seen as aisled roundhouses transformed into rectangular form (Harding 2009, 276)?

Elsewhere in Scotland the evidence of buildings in the first millennium AD is minimal after c.AD 200, and has even been suggested to represent a ‘tableaux of desertion‘ (Hill 1982, 10). There is some evidence of rectilinear forms  (Pitcarmick type houses, Anglian halls). Cellular forms also occur (e.g. Ardestie; Harding 2004, 240-2), and the continuation of round and oval forms is in evidence(e.g. Buiston (Crone 2010), Easter Kinnear (Driscoll 1997), and the circular ‘homesteads‘ of Perthshire). This reduction in evidence may also reflect a possible change to non-earthfast building techniques. Whatever the cause of this apparently sharp diminution of structural settlement evidence, it means that obtaining a coherent idea of the range of settlement forms present and the social structure that lay behind them, is going to be profoundly challenging.

Some extensive building forms

Stone-built ‘hut circles‘ occur extensively across Scotland,in ‘upland‘ contexts on the mainland and on the inner isles in Bronze Age and Iron Age contexts, though not in parts of the south-east or on the Northern and Western Isles. They occur in both Bronze Age and Iron Age contexts.

There is little variety of structural forms detectable from the visible remains in the west of Scotland, but there is far greater variety and more extensive groups are visible in the east. Excavation suggests that the majority belong to the second millennium BC, with a smaller proportion indicating activity in the first millennium BC (Halliday 1999, 56-8).

Crannogs and artificial islets are distributed across Scotland where conditions are suitable, with Late Bronze Age/Early Iron Age dates for the earliest recognisable timber crannogs and artificial islets constructed on a large scale during the period c. 800-500 BC, which has been termed the ‘crannog event horizon‘ by Cavers (2006). Regional distinctions have been proposed by Henderson (1998), based upon visible characteristics, although the value of this classification has been questioned by Harding (2000), particularly in terms of the relationship with island duns. Crone (2000, 4) understands these regional differences principally in terms of the availability of raw resources rather than as cultural differences. She notes that currently known distributions may reflect research bias (Crone 2000, 2), except for the situation in the south-east of Scotland where there appears to be a genuine dearth of crannogs, probably largely due to the relative scarcity in this region of suitable locations.

Regional trends

Broad regional and local patterning of the house and settlement record has been clear for decades, and underpinned Piggott‘s (1966) justification of the delineation of his provinces and regions. There is a broad distinction between the stone roundhouse forms of north and west Scotland and the timber houses of south and east Scotland, where the greater diversity of building structural form may imply the existence of a more complex or more varied society (Armit 2002; Henderson 2007a, 126-7). However, there were timber roundhouses in the former area, and stone ones in the latter. Distinct regional identities probably exist, but there are few well defined boundaries to distributions, and much transgression (Haselgrove et al. 2001, 23). Cunliffe (2005, 73-5) makes a broad distinction between Atlantic and western Scotland as a dominated by strongly-defended homesteads of single family units, and southern and eastern Scotland as a hillfort-dominated zone interpreted as reflecting communal activity of large groups of people. This population is based upon a range of other subsidiary settlements, in an acknowledged over-simplification, masking intra-regional and local diversity (see also Harding 2006).

Different levels of archaeological survival are, broadly speaking, the product of an east versus west, lowland versus highland, timber versus stone divide. Better preservation of stone architecture in the west allows us to understand the characteristics of buildings, sequences and change over time better than the, often, plough-truncated remains of timber roundhouses in the eastern lowlands. In the south-east the unique preservation of timber structural traces in the resilient turf of the Cheviot Hills has, to some extent, counter-balanced this tendency and excavations at Kintore (Cook and Dunbar 2008) have shown that when examined intensively on a large enough scale developments over time in roundhouse form (ring-ditche and ring-groove) can be traced. Burnt-down houses present a particularly valuable resource, as Barber’s analysis of the Bronze Age example from Tormore (Arran), Hodgson’s  work on the later Iron Age one from South Shields (Tyne & Wear), or Sharples’ analysis of the burnt layers at Scalloway, amply illustrate. This does require considerable investment in careful excavation and analysis.

Macinnes (1982) outlined broad changes in the character of the settlement record in eastern Scotland as evidenced from the largely untapped cropmark record at that time. This, she saw, could reflect contrasting types of social organisation, land tenure, or political centralisation. The complexities of the topic have been explored, inter alia, by Davies (2007) and Cowley (2009), and remain a key area for research; extensive areas of the cropmark record are essentially unsorted (e.g. the Moray Firth; though see Jones et al. 1993).

The idea of houses as cultural and chronological markers in the Tyne-Forth area proposed by Hill (1982b) has been applied in Eastern Dumfriesshire to ring-ditch houses (RCAHMS 1997, 161-2). It does not, however, seem to be applicable for other areas - e.g. the North East (Kintore - Cook and Dunbar 2008; Dunwell and Ralston 2008).  Atlantic Scotland has seen contentious debate over chronological and social associations, despite a long history of investigation and very distinctive remains, and the question of development over time remains contentious. For most non-Atlantic areas (with the possible exception of East Lothian) the chronological control is currently inadequate to allow the use of house plans as type-fossils.

There is a continuing need for the definition of local types and sequences.

Burnt-down houses represent a particularly valuable resource which needs to be seized with careful work in the field and in the lab.

Large areas of the cropmark record remain ripe for analysis, preferably in an integrated approach with upstanding monuments and excavated data.

Transmission of architectural ideas over space and time

Atlantic roundhouse types may have developed at different times in different places, with the Northern Isles considered a likely candidate for early development by most researchers (Armit 2003), while others prefer the Atlantic West/Argyll as an 'origin point' (e.g. MacKie 1992, 2002, 2008). The role of maritime links is of prime and indisputable importance here, enabling the transmission of knowledge and architectural preferences, within social contexts that must at present remain uncertain. The evidence to date can be interpreted as reflecting a migration of ideas and people into the Western Isles, and a similar line of arguments are used to suggest that wheelhouses were adopted in the Western Isles as an exotic import. again from the Northern Isles (Armit 2006, 252). Conversely a western origin is proposed by MacKie (e.g. 2008) based upon his interpretation of the evidence. This whole area remains one of active debate.

Other architectural styles or concept are similarly widespread in space and time. Souterrains vary in date from the Late Bronze Age/Early Iron Age in the Northern Isles to the Roman Iron Age south of the Forth, with a presumed floruit in the last centuries BC and first two centuries AD (Armit 1999; Miket 2002). There are differences in construction and dating across the areas of occurrence, but similarities in conception, situation and material assemblages imply links in terms of their function and behaviour. Composite ritual and storage functions (Henderson 2007a, 142-7) have been argued although such a composite functional interpretation may not be sustainable for all areas (see Dunwell and Ralston 2008 on Angus souterrains versus Carruthers on Orcadian examples).

Ring-ditch houses may be a further example of longevity accompanied by gradual transfer over territory. They appear to be present for up to a millennium north of the Tay before they are documented south of the Forth, (although there is the possibility of a visibility or research bias here, and the nature of the ring-ditch and its formation remains a key question). A parallel issue is the re-use or re-invention of crannogs across much of the first millennia BC and AD (and into the medieval period).

It is also clear that the migration of these different building traditions was accompanied by the independent growth of local 'sub-styles' wherever they passed. There are good examples of local distinctiveness within these architectural 'streams'. For example, wheelhouses in Shetland can be argued to be distinct in design from those in the Western Isles (Harding 2009, 112-4). In turn both areas are quite distinct from Orkney, where classic wheelhouses are absent, but where there are buildings with radial partitions (e.g. Howmae), suggesting that wheelhouse traits did penetrate the archipelago and so the total distinction drawn may be overemphasisied (Harding 2006, 74; Henderson 2007a, 160). At Scatness in Shetland wheelhouse use extends into the second half of 1st millennium AD, albeit with significant structural differences to earlier forms (Dockrill 2003, Dockrill et al. 2010).

Complex Atlantic roundhouses on Barra and North Uist are also considered distinct from their counterparts on South Uist (Armit 1997 a and b, 2002; Sharples and Parker Pearson 1997). These arguably represent local variations (perhaps autonomous or hierarchical) among the societies of the Western Isles that adopted Atlantic roundhouse architecture. The Atlantic roundhouse does not equal an homogenous cultural background or social structure - people adopt architecture rather than architecture adopting people.

Non-circular architecture

The Iron Age is not simply a time of roundhouses in various forms. Rectangular structures of four or more posts are often found on cropmark sites, and interpreted as granaries on no strong evidence; one could equally construct a roundhouse from a four-post structure. The nature of these structures remains a major concern. 

There is a variation in circularity, with a number of structures notably oval , while the concept of the ‘semi-broch’ introduced by MacKie , a D-shaped structure, remains open for debate; other scholars have seen it as the result of erosion . Recent work in East Lothian has suggested that here the development of non-roundhouse buildings was underway in the 2nd-1st century BC at the site of Phantassie  . This site also serves as a useful reminder of survey bias, as it was unrecorded prior to invasive fieldwork, and the cellular structures had no earthfast foundations. At Phantassie they survived because they used stone – but similar buildings of turf would leave no trace, and such ‘invisible’ architecture poses a serious challenge . For those who want a more hierarchical Iron Age, the landless peasantry may have lived in exactly such hypothetical turf or timber houses which we would struggle to recognise.

  1. The contexts, chronology and significance of the introduction of rectilinear forms of architecture in various parts of Scotland during the first millennium AD require a major input of future research and synthesis.
  2. What factors lay behind differing settlement size, and what it signified to live in a homestead, hamlet, village or hillfort requires further exploration.
  3. Issues of concerning raw materials and resource availability (particularly timber and stone) require further exploration, in both chronological and cultural terms, including comparisons between Atlantic and non-Atlantic traditions, but also more nuanced comparisons, including topics such as the South-east vs. South-west chronological distinction in timber usage for buildings (RCAHMS 1997), and the role of South-west timber into the Roman Iron Age and including the construction of some big very large buildings.