The life of a post-hole

with Kim Darmark

Digging post-holes can be rather tedious, non-rewarding work. Cut through, photograph, document the section, take samples and on to the next one. To a certain extent, this has been true at Kvarnbo as well, but a surprising number of the post-hole remains have, on the contrary, been challenging and exciting to investigate. This is due partly to the fact that so many of them have a life history which is possible to reconstruct. It is often possible to follow the events that have taken place through the different constructional elements making up the feature. In quite a few cases, it is possible to see the edges of the original pit, filled with a lighter primary fill, which was deposited in the pit at the moment of its construction. This fill is often lined with stones, creating a solid base for a beam to rest on. Both naturally rounded stones from the surrounding and rugged, fire-cracked blocks of stone have been chosen for this purpose. The primary fill contrasts markedly from a darker secondary fill, which enters into the pit at a considerably later date, when the old supporting beam is removed from the pit. The darkening of the fill represents many years of intensive use of the site, during which large amounts of organic remains have been tossed on site, creating refuse layers, usually referred to as cultural layers. This dark soil only infills the small chamber that is produced by the stones in the stone packing, and is often also rich in finds, which constitutes the other interesting aspect of post-hole investigation at Kvarnbo. Since we sift the soil through sieving net using water, we find every little find, even tiny ribs, scales and vertebrae from fish, which has ended up in the post-hole. The usual finds are bones and pottery, but a few less common items have been found as well, such as pearls, and small copper loops. Almost every feature that has been investigated this season has contained at least a few finds, some of them large amounts, and gives testimony to the richness of the cultural layer once present at the site.

Press this link to see the 3D model of feature 211 during investigation 😉

Traditional Strategy and New Techniques

by Frands Herschend

Strip (off the plough soil), map (the patterns you see) and sample (material from mapped structures) – is an archaeological field strategy applied to settlement remains in agricultural land, where crops have been growing for centuries. Ultimately, the method has become prolific, because of the gradual shift in the use of the cultural landscape. This shift made arable land more important and organized not least by means of roads. Consequently, farms were moved out of the farmland when possible. In Iron Age, on the other hand, arable land was less important, while grassland and meadows contributed substantially to subsistence. Not surprisingly, a rational Iron Age farm situation was in the centre of the farm’s agricultural area. Few roads were needed.

In Kvarnbo, change has been model, and today, the farms at Johannisberg are situated next to and above the arable land in which the Iron Age Kvarnbo hall stood on its small drained hillock.

When the excavations were planned, the strip, map and sample method was the obvious choice. But there are different way of stripping, mapping and sampling, and at Kvarnbo we have introduced a new mapping method in order to develop the general method. The testbed was successful during the test excavations in 2014, and in 2016, this mapping method was developed to become a routine.

Except for a handful of GPS reference points defining some of the test pits before the excavations started (see here), nine main reference points were defined after the top soil was stripped off in the area of over 1000 m², and complemented with 183 reference points inside of that area. Supported by these, all (georeferenced) exact measurements, plans and sections are based on photographic 3D models. Also, a large scale plan was made with a drone during a 10 minute photo session and its orthographic projection, printed as an overview, has enabled the team to orientate itself on the site.

Archaeological documentation goes hand in hand with interpretation. Description dominate fieldwork without excluding interpretation, and in the field, ocular observation is the general mode of perception: either you see something of you don’t. Later on, during the report writing process, interpretation and lab results dominate in order to answer the question: what cultural phenomena have we excavated? The problem in field archaeology is not what one observes, the problem is that which cannot be seen.

In this section from the trial excavations of 2014, one can see archaeological features from Late Iron Age (A12 and A13) been transected by more modern plough furrow (A18).

For instance, looking at plough layer and plough furrows or any other depression, the point is to describe some sort of “ploughing biography” of the field as a part of the its involvement in history. It is easy to see the dark furrows when they cut into the yellow underground, but difficult to detect them at the bottom of the plough layer, and impossible higher up, although they may well exist in soil 20 centimeters or more below the surface. In fact, only by means of close observation of soil sections can one distinguish between ploughed and not ploughed soil.

Since we want to sample the contents of the different fills in postholes, we make a preliminary section of the first centimeters of the soil until, based on this section, we can dig away the plough soil, that is, the contamination of the prehistoric fill. As a result, we can, for example, conclude that the burnt clay, which represents burnt walls and was abound in the test pits, doesn’t exist in the postholes of the hall (because it was never burnt down).

So far, we have sectioned, described and interpreted c. 230 features of 273 on the c. 1000 m² of our site. This is time consuming, but the ensuing 3D documentation is fast. On average, therefore, a team of four professional archaeologists and 2-3 amateurs can section, describe, interpret, sift and model 20-25 features per day, and sample soil for chemical and macrofossil analyses. 3D-modelling brings a new better and cheaper standard to strip, map and sample methods.

 

Post-holes

One by one, archaeological features at the Kvarnbo Hall site, mainly post-holes, are being investigated. And there is a number of really pretty ones among these post-holes – several are preserved much better than I expected (about 0,4 m in depth), and every so often, there is a stone packing evident. In at least three cases so far we have post-holes that have been filled with the material from a hearth and thereby filled with finds of bones from many different creatures (including fishes and birds) as well as pieces of pottery. Every  post-hole not yet investigated is therefore like an unopened package, whose contents are still unknown and it is up to us to unwrap the mystery 😀

Week 5 – brief summary

This week we had Daniel flying the drone over the cleaned surface, barely beating the rain, and giving us the much needed overview picture of the site. The overview picture confirms what we suspected – features are scattered over a large part of the trench and beyond the boundaries of our investigation. The majority seems to be circular post-hole like features very varying in size. A couple of centrally located features excite us with both their size, placement and relation to each other 😉 Some features can already at this stage be viewed as hearths and are mostly situated in the southernmost part of the trench. Otherwise, the surface is quite obviously dominated by plough furrows, hundreds of them, as well as a couple of long ditches transecting the entire site. We have numbered and individually photographed 246 archaeological features defined so far and have also started to make cross-sections through some of them. Investigating the features will dominate the rest of the excavation. Sadly, that will be done without help from Anton and Peter, both of whom have been with us 4 weeks and have proven themselves to be true troopers of archaeology – their effort was highly appreciated and will be missed. They left together with Jonathan and the remaining, diminished team thus has the fortune to investigate all the features no matter the weather 😀

 

250? 300? 350? archaeological features

There was an end to the endless manual cleaning of the trench 😀 and everyone involved in this job must be considered as heros!! This endeavor was by far the physically most demanding phase of our investigations. It was also quite boring. As a result, we have a swarm of archaeological features (criss-crossed by hundreds of furrows….). To my frustration, almost every time I wanted/started to photograph the cleaned parts of the trench, the sun made its appearance and there was my shadow again. Luckily, Daniel is on his way bringing the drone that will give us the much needed overview of the trench. It will be alright, you’ll see 🙂

The Mighty Hole

Soil stripping is finished! We have a trench of about 1000 square meters, of which roughly half is already manually cleaned and hidden under the tarp. There are three large mounds of soil surrounding the (mighty) trench (which are pretty good for taking overview shots 😉 ). The subsoil in the trench is quite varied; from a smooth yellow and clayish silt in the south to a  difficult and stony moraine in the middle and diabolically hard clay in the north. But archaeological features are everywhere! These are especially visible against the yellow silt in the southern side of the trench, while revealing them in the other areas requires extensive manual cleaning. Furthermore, traces of plowing are constantly present, easy to follow and generally oriented to the north-south… We have hundreds of features marked out using yellow wooden pegs. Of these a good amount will probably turn out to be just natural depressions, but many are clearly related to prehistoric use of the area. Joining these together to an understandable pattern is a challenge in which a bird-eye-view is crucial. This will be obtained through photographic 3D modelling and is the reason why we are eagerly awaiting the clouds to hide the ever-shining shine above our site 😀  

Week 3 – brief summary

Much has happened on the site during this week. Most importantly, we started soil stripping with the machine and managed to uncover roughly half of the intended area on and around the longhouse structure as seen on the aerial photo. Many different features appeared and even more become visible through meticulous manual cleaning. However, it is also apparent that the site is disturbed and we can clearly distinguish the effect of the plow which often has cut through archaeological features… At this stage, it is hard to tell which features are to be related to the Iron Age use of the area and the hall building(s), but it will certainly become clearer as we investigate further. Some nice finds surfaced this week as well, but these will be presented at a later stage 😛

Also, at the end of this week we are sad to say good-bye to a number of excellent people who had to return to their everyday lives. Thank you Hannele (and what a wonderful piece of art!), Kåre, Linnéa, Markus and Thomas – you all made a fantastic effort and you all will be missed!

It has not been just work though – the vikings from the Fornföreningen Fibula invited us to the kick-off dinner on Wednesday for this year’s Viking Market. Clothes were provided by Fibula and we looked spectacular with our mix of jeans, sneakers and linen tunics 😉 They (together with many visiting vikings) became our guests on Friday evening when the excavations were presented on the site.

To the left: we are visiting the vikings and thanks to Michaela, almost dressed up as vikings as well 😀 (Anton photographed with Thomas phone). To the right: vikings visiting us (Peter photographed with his own phone)

Results from the geochemical analysis

Finally, the results of the soil analyses are tripping in! In autumn, I sent quite a lot of soil from the longhouse site in Kvarnbo to Sweden to be analysed for plant macrofossils as well as for different geochemical properties of the soil; and, now, I have received the report from Samuel Eriksson from the Environmental Archaeology Laboratory at Umeå University. Samuel analysed 10 samples, ca 20 gram each, for parameters such as MS, MS550, CitP, CitPOI and LOI 😀 (you just got to love the abbreviations instead of lengthy explanations, don’t you!) – In any case, MS stands for magnetic susceptibility of soil, which reflects the presence of magnetic iron-oxide minerals resulting by burning, meaning that fire increases the magnetic susceptibility of soil. MS values are for the “natural” magnetic susceptibility of the soil in the original sample, while MS5500 values stand for the results after heating the original samples at 550 °C in the laboratory. Laboratory-induced heating is executed since the magnetic susceptibility of soil may be naturally high or low without connection to anthropogenic processes and laboratory ignition is kind of reference to the original samples. Simply put – this analysis tries to find out if the site/feature has been affected by fire. CitP and CitPOI are related to phosphates – both the organic and inorganic fractions, where CitPOI gives a reading of the sum of inorganic and organic phosphate. LOI stands for the amount of soil organic matter. Basically, these analyses try to find out if lots of organic waste has been deposited on the site or in a certain feature. And, below, you can see the results:

What does these “pillars” say? Well, one of my main questions while sending in the soil for the geochemical analysis was to find out which features have been affected by fire and which haven’t, in order to, among other things, separate different features from one another and find out if the longhouse has been burned or not. And the answer is in the MS values – features connected to the structure of the house interpreted as a feasting hall do not show traces of being burned! However, as you can see, two features deviate from the general MS pattern and can be seen affected by fire and at least in case of one of these features, I do wonder if it represents the bottom of a hearth? These and LOI values will be interesting to relate to plant macrofossile analysis results when I get hold on that report as well.

Feature sections’ overkill

I’m a bit sorry for posting this picture, but, these sections, the digitalized versions of these do look kind of nice (?) 🙂 and digitalizing these arcaeological features from 3D models (and not from the photos on this picture) is what has occupied me for the past few days. But, now, this work is done (wohoo!) and I am determined to get my site report largely finished by the end of this week.

Site reporting

After having been digging and writing tens-and-tens of technical site reports for the past 10 month, how much fun do you think it is to write another site report?? Even if it is a site report on the archaeological investigations at “my own site” of Kvarnbohall? Well, let me be frank, not so much fun… or, maybe, just marginally fun. Site reports are, after all, quite boring to write as it is mostly about technical data. Although, site reports are, at the same time, also, one of the most important kinds of archaeological writing. Anyway, I am back to working with the excavation data from the investigations at Sa 14.9. When it comes to this particular site reporting, I managed to do a lot during the autumn already, but, apparently, I then started from the simpler end and have to deal with all the complex issues now… Todays “headache”, for example, is the section below – the cut was placed through two features, feature 3 = the wall and feature 4 = post-hole, but the section revealed at least 4 different features, which I had, in fact, documented during the excavations already, but digitalizing the data was, nevertheless, not easy; despite the fact that I had my 3D models and a quite a number of photographs and my own excavation diary entries to aid the work… 11 sections digitalised… 10 sections to go… sigh?