536 and all that – the Gilltuna case

6 October, 2014

Gilltuna omslagThis week On the Reading Rest I have a report in Swedish from the excavation of a small village in Västmanland, Gilltuna, in the western outskirts of today’s Västerås. It is the westernmost of three Iron Age settlements, situated east, south and west of an open area of meadows and grassland. Skälby, Väster Hacksta and Gilltuna have been excavated during the last 20 years because the Västerås has grown. The area was colonized in the Late Bronze Age and settlements expanded during the centuries around the beginning of the Common Era.

Sundkvist, A. and Eklund, S. 2014. Gilltuna – där man följde traditionen. Den första storskaligt undersökta tuna-gården. SAU rapport 2014:4. Acronym: ASuSEk.

Gilltuna fig 00

Since the whole Gilltuna settlement area has been excavated, archaeological and historical source materials can be brought together allowing us to follow the development of the area and its settlements during 2300 years up and until today.

From Maja Eriksson’s chapter on the historical maps we learn that today’s Gilltuna is a small farm established in 1628 (ASuSEk, Eriksson:14 ff.). It was called Gilltuna because it was situated on or adjacent to farmlands that were called ‘Gilltuna’. This estate was first mentioned 1384 when it was still relatively large. Gilltuna might have been an estate without farm houses already then and soon it was split-up and farmed by neighbouring landowners and tennants. On the cadastral maps from the early 18th century, nevertheless, ‘The Gilltuna fields’ have been marked out exactly where the archaeological excavations found the remains of farm houses that had been used until the Late Carolingian Iron Age (LCIA, late 10th century). Remains of the Early Medieval farm houses have not been found, and they might very well have been destroyed by ploughing, but the excavations showed that there were still two farms in the village in the 10th century. In 1384 there was obviously just one estate. The two CIA farms go back to what was originally a single Pre Carolingian Iron Age (PCIA) farm situated inside a stout enclosure, i.e. a ‘tun’ in Swedish (ASuSEk:135). The suffix ‘-tun’ is similar to the suffix ‘-ton’ in Anglo-Saxon place names such as Brighton – Beorhthelmes tūn in Old English. There are many kinds of enclosures and as a place name ‘Tuna’ (plural of ‘tun’) may stand alone. Moreover, when combined, the meaning of the first part of the names varies considerably.

Gilltuna fig 04In Gilltuna, the enclosure is a prominent feature measuring c. 44×44 metres or 144×144 feet. It is a formal enclosure and a plot respected and maintained during hundreds of years. From a purely practical point of view it is a rather pointless restriction, which makes the manifest significance of the enclosure all the more important. This enclosure is connected with the revival in the Late Iron Age (LIA) of the Early Iron Age (EIA) village. This latter village was replaced by a rather large farm, which in its turn was accompanied by a small croft 40m south of the enclosure close to the brook. It seems reasonable to suggest that something radical happened in the settlement and this event in all probability resulted in a farm called Tuna or perhaps Gilltuna. The first part Gill- may refer to people feasting together (ASuSEk, Engström:200). In that case they would have been doing it in the large house behind the enclosure rather than on a farm marked by subsistence economy.

Based on 51 14C-dates ASuSEk divide the settlement into eight phases. The settlement starts with one or two farms spread out in the area. There is a time gap between the first and the second farm in the area and that suggests that to begin with, when it came to farm houses, there was no continuous presence in the area. But already in the Late Pre Roman Iron Age (LPRIA) there were several contemporary farms in the area. By then the settlement had become a small village with an ad hoc structure visible as a number of farm sites not always boasting a farm. This is the expected settlement development.

Around 500 CE the 14C-dates indicate that there was a hiatus in the central part of the settlement and after this break the -tuna farm was erected. ASuSEk discuss the 14C-dates, and find that the hiatus in the central part of the settlement is a plausible interpretation. Nevertheless, the Gilltuna area as such was not completely abandoned. In the easternmost part of the settlement in an area mostly used for outdoor purposes there was a small cottage with a fire place dated 1531 bp +/- 30 and a date, 1574 bp +/-30, from the well just outside the house. The size of this cottage is c. 60m2, with a 24 m2 dwelling room, a small central entrance room and perhaps a cowshed similar to the size of the dwelling. This is quite possibly a small croft and at the time the only inhabited building at Gilltuna.

Gilltuna fig 01When we look at the remaining 49 14C-dates as a general probability distribution they seem to fall on three parts. An intuitive analysis of 14C-dates from Gilltuna, therefore, suggests that there was an initial presence in the PRIA (Phase 0), a permanent phase from the end of the LPRIA to the EPCIA (Phase1) and a third Phase commencing in the LPCIA and coming to an end in the LCIA (Phase 2).


The possible time gap between Phase 1 and Phase 2 merits a more formal analysis because this break seems to fall in the middle of the 1st millennium CE, and a period characterized by radical change also in Scandinavia. Usually we do not see this kind of hiatus and re-settlement in excavations, because generally speaking a settlement given up in the middle of the 1st millennium was demolished and/or incorporated into more prosperous villages in the given settlement area. Usually these villages survived into historical times. Since Gilltuna is an exception to this rule, it would be interesting to know more precisely when the re-settlement took place.

Consequently, if we turn to the representation of the phases in the central part of the settlement, as singled out by ASuSEk, it becomes natural to ask when Phase 2 commenced and when Phase 1 came to an end. There is in other words good reasons in the archaeological context and its 14C dates to consider it a fact that in the first part of the first millennium CE there were two different settlement phases at Gilltuna – a 1st phase followed by a 2nd phase.

Thus the first question to be asked is whether there was a hiatus between the two phases? To answer this question I will use BCal – an on-line Baysian radiocarbon calibration tool (1).

To begin with we want to know the probability that the data set, which dates Phase 1, is indeed earlier than the corresponding data in Phase 2. What BCal returns is an estimate of the probability that the event represented by beta 1 (i.e. the modelled end of Phase 1 consisting of 30 14C-tests) is earlier than the event represented by alpha 2 (i.e. the modelled beginning of Phase 2 consisting of 19 14C-tests). The probability is 0.968313. We can in other words safely conclude that Phase 1 came to an end before Phase 2 commenced.

Including this as a fact in our modelling we will re-define Phase 1 as definitely earlier than Phase 2. Since this is now true the query: An estimate of the probability that the event represented by beta 1 is earlier than the event represented by alpha 2 returns the probability 0.9995472.

Gilltuna fig 02Based on this model we can proceed and ask ourselves what ‘earlier than’ will mean in terms of a time gap or hiatus. BCal will model the ‘posterior probability distributions for an estimate of the time elapsed between the events represented by two parameters’. In our case these parameters are once again Beta 1 (the end of Phase 1) and Alpha 2 (the beginning of Phase 2). We will set the significance level to 0.95 and ask BCal to estimate the lapsed time between highest posterior density intervals (HPD intervals in years) for Alpha 2 and Beta 1. The estimate is 25 to 182 years. This means that we must think of a hiatus of 25 years and probably more.

Having drawn this conclusion we can proceed and try to relate the settlement phases to The Cold Decade 536-545 CE (TCD). This decade is important because it could have caused the death of a large part of the population (cf. OtRR 18 mar 2013). We ask: what is the probability that the event Beta 1, i.e. the end of Phase 1, took place before the year 536 CE and the volcanic eruption that is supposed to have resulted in a cold decade?

The probability for that is 0.9795934 and we must thus conclude that Phase 1 came to an end before 536 CE. Actually it is very likely (probability 0.90254027) that the hiatus started before the 500 CE.

What then is the probability that Phase 2 commenced after TCD, i.e. after the year 545 CE?

The probability for that is relatively low, 0.756811, but it is nevertheless more likely that the new settlement commenced after 545 CE than before. Bearing this in mind we can ask BCal to return the possibility that that Phase 2 had not commenced 600 CE. That probability is as low as 0.061325524.

If we sum up the modelling so far we have established (1) that there was indeed a gap between Phase 1 and Phase 2 and (2) that Phase 1 came to an end well before 536 CE. It seems that Phase 2 commenced after 545 CE, but it is not obvious. It is much more likely, however, (3) that Phase 2 commenced before 600 CE. In the next step in the modelling we will take this latter possibility for granted and introduce what BCal calls ‘a floating parameter, Phi 1’. In this case Phi 1 is the year 600 CE. In the model, therefore, it becomes a fact that the calendar year 600 CE is absolutely posterior to the beginning of Phase 2 – the event Alpha 2 modelled by BCal.

Adding this parameter to the model, we may once again ask about the probability that Phase 2 had commenced a certain year CE. The effect of the floating parameter can be seen in a diagram.

Gilltuna fig 03

Comparing the two models (with or without a floating parameter) to each other it becomes plausible that the large farm characterizing the beginning of settlement Phase 2 was established within a generation after TCD. It may have happened earlier, but that is not likely. The growth in probability 550 to 570 is probably indicative of the beginning of Phase 2 and dates prior to 530 have low probabilities.

It seems reasonable, therefore, to conclude that in the EIA ‘Gilltuna’ settlement, whose real name we don’t know, crisis became a fact in the EPCIA well before TCD. This amount to saying that the first stable settlement period (Phase 1) with several contemporary farms probably came to an end before 500 CE. Around 500 CE, a period in which the calibration curve is more or less horizontal, a small peripheral cottage, c. 60m2, with a 24 m2 dwelling room was the only standing building in the area (cf. ASuSEk:68-69). After this abode and TCD had disappeared, i.e. some time between 550 and 580 CE, the ‘tuna’ farm, perhaps Gilltuna, had become a fact. It might well be that events in TCD triggered the foundation of the ‘tuna’ farm, but in that case, crisis prior to this decade had already emptied the settlement paving the way for the takeover, which might or might not have been unfriendly to the crofter in the eastern outskirts,

Gilltuna is interesting because it is a god example of an excavated place name. The ‘tun’, the enclosure, is difficult to miss and owing to the hiatus it is fair to suggest that the ‘tun’ at Gilltuna was a mid-millennium invention organized as a takeover of an abandoned or almost abandoned agricultural area. The enclosure marks a new regime. This kind of takeover or re-establishment of a settlement is not unique. On the contrary, seen in relation to the many abandoned RIA and EPCIA settlements, this was probably what happened in most of the settlement areas. The vast majority of the settlements were abandoned, but the better ones were successfully re-established and contract archaeology has had no reason to excavate them because they are easy to avoid when exploiting a landscape creating industrial areas and suburbs. The specific character of Gilltuna is thus not the EPCIA abandonment. Instead, it is the abandonment during the Early Middle Ages (EMA) – that which robbed us of a village rooted in the LIA – that is noteworthy. This abandonment and urban expansion combined 2010 giving contract archaeology an extraordinary possibility to excavate a relatively large settlement that was given up in the Middle Ages. Contract archaeology brought the excavations to a successful conclusion.


The BCal team comprises Caitlin Buck, Geoff Boden, Andrés Christen, Gary James and Fred Sonnenwald. The URL for the service (http://bcal.sheffield.ac.uk). The paper that launched it was Buck C.E., Christen J.A. and James G.N. 1999. BCal: an on-line Bayesian radiocarbon calibration tool. Internet Archaeology, 7. (http://intarch.ac.uk/journal/issue7/buck/).



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