showing the position of buildings S1 and S9, discussed below.
Excavating sites can be interesting, exciting, and urgent. It’s a social activity conducted in the great outdoors, usually near a pub. Writing reports is in many ways the complete opposite: it can be a solitary, boring, and a frustrating task, especially with no decent pub -- as I was to discover when I was given the job of writing the Orsett ’Cock’ excavation report in 1989.
To judge by the size of the S9 roundhouse, the site was ‘high status’. As if to prove the point, and almost certainly in response in the Roman invasion, the site was fortified with extra ditches, palisades and a defensive gate. This involved quite a lot of manpower, timber, and general upheaval. It is only with the benefit of hindsight that the futility of trying to defend such an installation against a Roman army that was merrily knocking off hill forts like Maiden Castle becomes apparent -- but an Englishman’s home is his multivallate enclosure.
A tantalising glimpse of what befell the Orsett enclosure was the find of a group of six spear heads at the bottom of one of the ditches, which had been rapidly back-filled; this may suggest that they surrendered, but that's a story for another time.
The process has its own rewards; you make your own discoveries as you excavate the archive, effectively re-excavating the site, and freed from any prior emotional or intellectual involvement, you can take a very dispassionate look at the evidence. Exciting – you bet it is! But it's more like reading a detective story than skiing down the Matterhorn; Orsett made me realise there is a whole library, with hundreds of sites, thousands of features, all yet to be explained. The ‘following up of clues’ is only aspect of the previous analogy that is valid, because ultimately you are the author and you have to solve the crime yourself.
So how do you go about writing an archaeological report? It is quite possible to write a perfectly acceptable archaeological report with a minimum of interpretation, simply presenting the evidence and referencing similar archaeology on appropriate sites. In this way we borrow other people’s interpretations, and subtly avoid any individual responsibility, the principle downside being that a lot of evidence may go interpreted.
However, this is for posterity, so it pays to be conservative, and as we have discussed, there are standard types of structures, such as roundhouses and four-posters made up from standard features that can be universally recognised, which require little further explanation. There is a danger that, like bent coppers checking each others version of events, archaeologists have colluded to create a version of the evidence, complete with artistic reconstructions of the usual suspects.
I had inherited the excavator Hugh Toller's account, written shortly before he left archaeology, in which he duly identified the main structures and major features and put them in ‘phases’. His account still left the majority of the features unexplained, and besides, giving a group of them a label, such as ‘roundhouse’, is a long way short of understanding them.
B: Conjectural wall; C: Main ring beam; D: Inner ring beam
The gully F19, defining S9, was also polygonal, particularly on its inside edge, and I reasoned that this must reflect the shape of the wall. The outer set of the two circles of postholes I interpreted as ring beams had only 10 posts, so the roof would not be that circular. Therefore I set the conjectural polygonal load-bearing wall next to the gully, but far enough away for it not to collapse into the gully. I could relate the wall's corners to the other components geometrically, and create a hypothetical structure that worked. The additional postholes in the interior were interpreted as resulting from alterations or repairs, some being temporary props for the structure, and the position of the rafters was inferred on this basis.
This and many aspects of the report was the product of a year’s analysis, and was as far as I could get in the time available. Much depended on the interpretation of F19 as a drainage feature, but it never quite made sense; the gravel soil at Orsett drained fairly well, so F19 could be a soak-away, but it had a volume of 20m³, enough to hold a month's rainfall running off the roof all at once.
As with my predecessor, Orsett was my last serious contribution to archaeology, and, after a largely unsuccessful attempt to sell the concept of CAD, computing, and structural analysis as a commercial consultancy to an incredulous archaeological world, I decided to sell skills to mammon in 1991. But I took with me the archaeological plans and the reports that had intrigued me, just in case I got bored – there’s no mystery in making money.
When, laden down with years of research into building analysis, I returned to archaeology, it had changed – it was now all commercial consultancies using CAD and computing. However, interpretation and structural understanding had not progressed very far. There was a brief moment of panic at university when a tutor said, “at least now we understand roundhouses” – till I realised they were talking about one of Mike Parker-Pearson’s theories. 
The trench was polygonal in plan, and the section showed a roughly semi-circular dark stain, in a feature of variable depth, entirely consistent with a foundation trench for a log-built wall that had rotted in situ. Besides, the feature was cut into boulder clay; and water draining very slowly or evaporating would have left horizontal laminate layers, formed of clay particles. To argue that water dripping off a roof could create a feature penetrating over half a meter into a boulder clay subsoil is frankly preposterous. You don’t really need to have a roof – dig a hole like that in many soils, especially in winter, and it will fill with water of its own accord
I am happy to confess that nearly 20 years ago, under the influence of older wiser heads, I mistook the feature F19 at Orsett for a drainage feature, when it was really a trench wall foundation, for which I am very, very, sorry. By way of repentance, and with all the respect due to an old, much loved, but ultimately facile interpretation, I am going kick the concept of ‘drip gully’ as hard as I can in its intellectual nuts, and jump up and down on it till it stops moving.
Water goes downhill; it's done so since God was a boy, and that is how drainage works. You take water, a highly destructive and undesirable agent, away from your built environment under gravity. You do not, unless you are particularly stupid, encourage the water to drain away next to a building with timber foundations and walls largely made of mud. Nor do you allow it to form or dig a trench deeper than your wall foundation right next to your building.
With Orsett S9 we find ourselves very near the end of the roundhouse tradition in southern England, and since we have covered a lot of comparatively new ground in the last few articles, it is worth sketching out some general conclusions.
Graph showing the relationship between the number of posts in a ring beam and its diameter. (Ring beam diameter is used because it should be proportional to the size of the building’s roof, and wall or roof diameter are often archaeologically invisible and not available.)
- In the first millennium BC, post-and=lintel engineering was rational and schematised, as evidenced by similarities in post loading and ring beam design, and amply demonstrated by the graph above.
- Probably in response to a need to increase the functionality and flexibility of roofed interior space, the loading on posts was increased as better perceptions of safe loading were gained through experience (e.g., Little Woodbury & Pimperne Down).
- By the Middle Iron Age, buildings with polygonal load-bearing walls had developed, probably log built, which reduced the need for interior posts still further (Orsett S1/S9).
Sources & further reading:
 G. A. Carter, 1998: Excavations at the Orsett ‘Cock’ enclosure, Essex, 1976. East Anglian Archaeology Report No 86.
 M. Parker Pearson, 1999: "Food, Sex and Death: Cosmologies in the British Iron Age, with Particular Reference to East Yorkshire." Cambridge Archaeological Journal, 1999 pp 3-69
 TWM Archaeology. Unpublished Grey Literature.
Graeme Guilbert, 1981: "Double-ring roundhouses, probable and possible," in Prehistoric Britain. Proc Prehist Soc 47 & G. Guilbert, 1982: 'Post-ring Symmetry in Roundhouses at Moel y Gaer and some other sites in prehistoric Britain', Structural Reconstruction - Approaches to the interpretation of the excavated remains of buildings, British Archaeological Report 110, BAR, 67-86."