Publication Account

Date 2007

Event ID 586658

Category Descriptive Accounts

Type Publication Account

Permalink http://canmore.org.uk/event/586658

Euan W Mackie Broch Corpus 2

NC40 4 TOR a' CHORCAIN ('Lang-well')

NC/4104 0088

This vitrified dun or massive round-house (of broch-like proportions and stand-ing on top of an earlier hillfort) is included here because it may be an example of how a broch-like structure –in the sense that it is a complex wooden roundhouse protected by a ponderous shell wall of stone – has evolved from quite a different pedigree. The site is on high ground overlooking Strath Oykell and its river and with wide views up and down it (visited during the excavations in 1974).

Excavations were carried out on the dun by Helen Nisbet in 1973 and 1974 [4]. A single trial trench into the west flank of the hillfort failed to reveal any vitrification but located two occupation layers under fallen rubble. Signs of the hillfort occupation – with a few artifacts such as stone rubbers, hones and a few pounders – were also noted at the base of some post-holes and elsewhere.

The excavator gives a fairly detailed account of the likely structure of the timber-framed wall, and also discusses the wider significance of the site [4,inc. Appendix]. Here however, after a brief description of the wall and entrance, we will concentrate on the primary wooden roundhouse, traces of which were found in the central court of the 'dun'. The fact that only about half of the interior was excavated is to be explained by the concentration of the work on sectioning the vitrified wall, a huge task [4, pls. 5 and 6]. The project was paid for by the late Mr S P Fay of Los Angeles who was interested primarily in the phenomenon of vitrification.

1. Situation

The dun stands on the higher, western summit of the hill and on top of the remains of the hillfort defences. Heavy vitrification was visible before work started. The structure was found to be almost circular in plan with an entrance facing east, an internal diameter of 15.0-15.5m and a wall averaging 5.0min thickness; the inner face of this still stood in places to a height of over 2m above the primary floor. On the basis of the quantity of rubble lying about the original height was estimated at about 3-4 m.

2. Description

The dun wall

The inner and outer faces were of well-coursed slabs, with a core of roughly laid water-worn cobbles having a central spine of solid vitrified stone. The original presence of some kind of timber-framing inside the wall was proved by the finding of beam holes containing charcoal. The burning of such a drystone wall laced with wooden beams is usually supposed to have produced the vitrified masses in the wall core [5].

The entrance passage

The stone walls of the entrance passage were 2.50m apart and the floor had been paved with transverse logs. Massive upright posts – four on the south or left (with a fifth in line with them just inside the dun) and three on the right – had been partly set into the wall (in vertical post slits) and must have supported a massive wooden entrance tunnel, presumably with some kind of tower on top and a wooden gate (no stone door-checks were found). The posts were presumably set in place before the stone walling was built and the excavator thought that they were likely to have been fastened to the timber framework in the wall core. There were signs that some of the posts had been pulled out, and the timber entrance presumably destroyed, before the burning and vitrification of the wall. No traces of stone lintels roofing the passage seem to have been found so doubtless the entire entrance structure was of wood; presumably this was connected with a fence or palisade which ran round the top of the wall near its front edge.

The guard cell

in the left wall of the passage is the opening to a mural chamber or guard cell, the upper part of the wall of which had vitrified; this had caused a slump of once-molten rock into the room itself. The chamber was 3.25m deep and about 2m wide, the entrance being 0.5m wide. There was no sign of corbelling in those parts of the vertical wallface which had survived (up to about 50 cm) below the vitrification. A thin black occupation layer rested on the subsoil and above this was a mass of carbonised logs, presumably the remains of the wooden roof capped with turf.

"The guard cell exhibits in miniature the entire vitrification process; well-built wallfaces passing upwards and sideways into vitrification, with cracking and bending of the stones, and mobile vitrified material appearing to 'ooze' between them. It leaves no room for doubt that in suitable blanketed conditions, stones do actually melt to give vitrified masses." [4, 56].

The interior

The stratigraphy of the interior provided evidence of a primary occupation on the old ground surface, then a layer of burning with collapsed roof material on top of this and, finally, traces of a secondary occupation on top of the ruins. A level platform with a very irregular surface was built up before the dun wall was constructed, and this was subsequently baked hard by the fire which destroyed the latter.

A ring of wooden posts was set up in the area enclosed by the dun wall, at a distance of about 4.0m from it; eight post-holes were actually exposed and the original total was probably fourteen. The holes were about 50cm deep but the size of the posts they contained was not estimated. The ring would have been about 8.5m (27.9ft) in diameter and must surely have supported the mid point of the roof rafters, the outer ends of which were presumably on the wallhead. No scarcement was found on the remaining inside wallface but if there was a raised wooden floor also attached to the posts these would surely have been attached to some of the beams which doubtless projected from the wall core.

However the burnt roof debris (below) formed a relatively thin layer and there was an absence of burned timbers from the central area of the floor which made the excavator think that the roof might have been a lean-to affair, with the middle of the floor having been left open to the sky.

Despite the uneven surface of the foundation platform the inhabitants seem to have lived on this, and a thin occupation layer, also baked hard, was found. However there were no artifacts inside "and there was a complete lack of evidence for normal domestic activities." [4, 60]; the interior had evidently been kept clean. Not a single sherd of pottery was found. There were some stone slab settings in this floor which might have been small hearths but one would normally expect a large central hearth inside a roundhouse of this size. It is possible that there was one which was not uncovered; the excavated areas could just have missed it, as they did at first at Rhiroy (NH19 3).

Traces of occupation were also found outside the dun and there was a distinct accumulation of midden material on the slope outside the entrance, which contained many fragments of the bones and teeth of sheep and cattle.

A layer of what appeared to be burned and collapsed roof material lay all over the outer part of the floor in the interior, forming a network of charred timbers, twigs and burnt turf. The charred stumps of several of the posts were found in position in their sockets. Between these posts and the wall lay a roughly radial pattern of fallen roof timbers mixed with turf, and the absence of such debris from the central area suggests, as noted, that the roundhouse had an annular, lean-to roof with a clear middle part.

There was evidence of two phases of occupation on top of the burned strata in the interior, implying that people continued to live there after the destruction and vitrification of the wall. The floor had first been levelled up with available rubble and debris which had fallen from the walls. Part of the interior at least was then apparently re-roofed using fresh posts, and occupation continued for some time thereafter (there are more details of this later habitation in the report).

3. Dating

Radiocarbon dates

A set of five C-14 dates was obtained for burnt material. No. 1 was for charcoal from a large post-hole at the entrance to the guard chamber; no. 2 for charcoal from the foundation course of the inner face of wall; nos. 3-5 are all for charcoal from a fallen roof timber. It was observed that the roof timbers tended to be full of beetle holes, suggesting re-used wood, whereas the post-hole timbers were not. In the absence of any indication of how the dated fragments related to the start of the growth of the trees concerned one can only assume that the C-14 dates relate to a time a little before the cutting of the timbers for use in the building.

1. GaK 4860 2210 +/- 90 (260 bc)

2. GaK 4862 2240 +/- 90 (290 bc)

3. GaK 4861 2200 +/- 100 (250 bc)

4. GX 3274a 1040 +/- 210 (ad 1010)

5. GX 3274b 2040 +/- 140 (90 bc)

Table of uncalibrated radiocarbon dates obtained for Langwell. No. 5 was obtained after no. 4 had been received.

Although the reliability of the early Gakushuin laboratory dates (GaK) has been questioned the three from that laboratory are reasonably consistent and match the second Geochron date well. There is no obvious explanation for the first Geochron (GX) date being so much later. Broadly speaking the four consistent dates, when calibrated, suggest that the timber-framed dun was built at some time during the 3rd or the 2nd centuries BC [4, fig. 10].

Thermoluminescence dates

After the excavation was completed Sanderson and others obtained a number of TL dates for several vitrified forts including Langwell [6]. One would expect that such dates, being performed on the vitrified material itself, would give an indication of when the stone was last heated – that is, when the dun was destroyed by fire. The date for Langwell has a mean age of AD 205 which suggests that the site was in use for several centuries. However other dates from vitrified forts vary wildly from the equivalent C-14 dates [6, 7] so caution over the interpretation of this one seems advisable.

4. Discussion

in many ways the size, shape and internal wooden structure of Tor a' Chorcain resemble those of a hollow-walled broch far more closely than, for example, the drystone roundhouse at Buin Orkney (ND20 3), and the site provides an interesting case study of how some form of complex, and perhaps two-storeyed, wooden roundhouse – enclosed by a strong defensive wall – emerged from the timber-framed hillfort tradition in the 3rd or 2nd centuries BC. However the internal diameter is, at 15.4m, very large and raises the question of whether it would have been possible roof such a structure completely.

5. Finds

There were large numbers of whetstones and hones, and also pebble hammerstones and grinders, all over the site and in all levels; most of these stone tools are now at Langwell Farm. Other finds were extremely sparse. It is not entirely certain what the 'scoop' is, or what 'hand mortars' are.

From the primary occupation levels came 15 hones and whetstones, 3 sling-stones, 7 rubbing stones, 1 scoop, 1 quartzite strike-a-light, 1 bone bead (from the floor of the guard cell), and an unidentified iron object.

From the destruction debris came 28 hones and whetstones, 3 sling-stones, 8 rubbing stones, 2 hand mortars, 7 pounders and a well-preserved iron blade [4, fig. 9).

From the secondary occupation layers came 11 hones and whetstones, 1 sling-stone, 26 rubbing stones, 4 hand mortars, 3 scoops, 1 pounder and a polished ring-bead of green serpentine.

in the topsoil outside the dun was found a fragment of a shale bracelet [4, fig. 9.1).

Dimensions (taken from the plan)

Overall diameter about 25.7m (84ft 3in), internal diameter about 15.4m (50ft 6in), wall proportion about 40%. This is a very large roundhouse by broch standards; Mousa in Shetland (HU42 6), for example, could just about fit inside it.

Sources: 1. NMRS site no. NC 40 SW 3: 2. H. Nisbet in Discovery and Excavationin Scotland 1974, 59-60: 3. H Nisbet in do., 1973, 48-49: 4. Nisbet 1996: 5. MacKie 1977: 6. Sanderson et al. 1988: 7. Alexander 2002: 8. Church 2002, 74-5.

E W MacKie 2007