Friday, June 22, 2012

0100 - Going public

I talked about this before: the archaeology of prehistoric enclosures (as all archaeology actually) needs to go public. In fact, its relevance (and the relevance of its professionals) critically depends in the capacity of produce some valued social return, and there are some interesting projects all over Europe working this way.

In Portugal, we are just beginning, and Perdigões is a leading project on that matter, assuming that research has its own funding future and social justification in becoming relevant to the general public. But we are also aware that its relevance depends back in regular research of quality.

So, at Perdigões there is a path that is being walked with conviction in social responsibility. And that has been noticed here and there.

Even Google caught us excavating last year (2011). It was the first week of field work. And we will be there again this year. Next week we will be preparing the excavation that will start at July 16th. You can fallow it then in its own blog (see the side bar).

Monday, June 18, 2012

0099 - Ditched enclosures in the Portuguese north hinterland

Ditched enclosures in central/north Portugal (Yellow circles). Santa Bárbara is number 30.

The actual distribution of ditched enclosures in Portugal shows a clear concentration in Alentejo region, in the Guadiana and Sado basins. But some enclosures with ditches also started to appear in the north part of the country. First in the littoral. But in the last years they were detected also in the hinterland, in Beira Interior.

Is the case of the ditched enclosure of Santa Bárbara, Sabugal (Peresterlo & Osório, 2005). Unfortunately there is not much information published about the site and its negative structures. Through some newspapers articles we know that there are pits and a ditch (25 meters long and 3 meters wide), apparently dating from the Chalcolithic.

The site is very near the Spanish border and that region of Portugal is part of the western traditional pathway between the two Iberian central Mesetas and a natural extension of the central territories, both north and south of the Central Mountain System. Well, in both areas, the Madrid region and the Douro valley, the last decades have revealed a significant density of ditched enclosures. Besides, the Beira Interior region is also well connected to the South, being part of that north-south route that links three mains river valleys: the Douro, the Tagus and the Guadiana.

It is a linking region, well marked in several historical periods (such as in the Bronze Age through stelae distribution), connected to areas where ditched enclosures are very well represented. So, it was just a matter of time before they started to appear here too. And more are expected for the near future.  

Thursday, June 14, 2012

0098 - Dating ditch fillings

Dates from ditches 3 and 4 from Perdigões. They are Chalcolithic ditches, dated from the 2nd quarter and middle 3th millennium BC. But in a top layer of ditch 4 we got a Late Neolithic date (a ditch that has to middle 3rd millennium dates for bottom deposits). A typical situation of incorporation of earlier material. In fact, just 3 meters away there was a Late Neolithic pit burial that was disturbed in Chalcolithic times. Taken from Valera & Silva, 2011.

Dating the fillings of ditches and interpret the results is a tricky issue.

First, we must be aware that we never date the opening of a ditch, only the beginning of its filling. And we do not know the time between the opening and the beginning of the last filling process of the ditch (I say last because we must considerer the possibilities of re-openings).

Second, what is integrated in the ditch filling may be older than the filling process or even older than the excavation of the ditch. In fact, especially in sites with long living periods (like Perdigões, for instance), where earlier materials can be about or the excavation activity is so intense that earlier deposits are constantly being remobilized, it is natural that some of the material that integrates a filling deposit inside a ditch is actually from earlier occupations. By dating this material we will not date what we intent to. We will be dating earlier material that has nothing to do with the time the ditch building or its filling moments. That is why sometimes we have earlier dates in top deposits and later ones in the bottom deposits.

So, how can we avoid these problems?

Dating ditch fillings implies dating series of samples, where outliers can be detected. It is not just the need of dating the sequence of deposits to determine the filling rhythm (which is, of course, important). Even if there are just one or two deposits, we must have more than just one date, precisely because of the problems raised by the typical dynamics and activities that take place in this kind of sites.

It is more expensive, I know. But one date in a ditch, except if you have a well defined and closed context (like a burial, for instance), is far from enough. And every date or series of dates need a serious critique, regarding the dating procedures, dated material, relation to context, nature of the context formation, post depositional events, and so on. Or we will just adding smoke to an already foggy area.

Bibliographic References:
Valera, A. C. & Silva, A. M. (2011), “Datações de radiocarbono para os Perdigões (1): contextos com restos humanos nos Sectores I e Q”, Apontamentos de Arqueologia e Património, 7, Lisboa, NIA-ERA, p.7-14.

Monday, June 11, 2012

0097 - How did they do it?

They did choose adequate bedrocks. There is a clear relation between Portuguese ditched enclosures and geology that enables an easier excavation. But making it easier doesn’t mean it was easy.

In fact, to excavate the ditches, that in South Portugal started at least in Late Neolithic (second half of the 4th millennium), they must have used the technology developed since earlier times: the technology developed in mining for flint or for minerals, like variscite.

I have already drawn the attention for the fact that there are several evidences of “transference of technology” in Prehistory, from some areas to others; from some kind of architectures to others. For instance, the building of the access corridor between walls to the inside enclosure of Castro de Santiago is clearly an application of megalithic building procedures.

So, to study the technologies adopted to open ditches it is in mining tools and in mining techniques that we might find a window. There is a clear interesting relation that can be established between the researches of these two Neolithic practices.

And the same can be argued about the hypogeal building tradition. There is knowledge and an assemblage of techniques and tools that must have had a transversal use in different building activities. Underground techniques of excavation are certainly earlier than ditched enclosures in western Iberia. They might have provided the means to the architectural materialization of some new ideas. Just like the megalithic “engineering” was certainly helpful for walled enclosures.

So, looking into mines, and mining material, might be useful when we study ditched enclosures.

Wednesday, June 6, 2012

0096 - The sunset of ditched enclosures?

Small inside enclosure with a burial pit.

When did the Neolithic and Chalcolithic type of ditched enclosures stop being built? Well, as the question suggests, it would have been at the end of the Chalcolithic, of course. In fact, at the present moment, no ditched enclosures like those are known to have been built in the second millennium BC. I recently have used this apparent situation to argue that the Neolithic and Chalcolithic ditched enclosures were related to a specific ideology (or cosmogony) and that they stopped being built in the beginning of the second millennium precisely because that cosmogony was structurally changing at the end of the third millennia (Valera, in press).

Well, the enclosure in excavation by ERA at the moment seams to reveal a relative late chronology, although every elements of the architecture also seems to be rooted in the Neolithic tradition. It is soon to be conclusive. But the pottery from the ditches suggests a late chronology in the third millennium and there are pits with pottery that clearly indicate the first half of the second millennium (Bronze Age).

The image, at the moment, is that the enclosures were built in a late Chalcolithic and that pits were still being excavated in the early Bronze Age. But the relations are still to be established. In fact, the inside ditch, the one that slides deeper from the gate to de back, is very small (just 8 m diameter inside) and has only one pit inside. Well that pit has an individual burial with three complete undecorated vessels and a Palmela point, indicating a moment of transition to Bronze Age. Is it a latter pit? Or this small enclosure was built to enclose that pit?

Detail of the burial excavation in a earlier stage. We can see the leg and the skull (and a stone over the neck).

It is soon to decide. But what this data is suggesting is that some of this Neolithic rooted architecture and practices might have reached the beginning of Bronze Age. In a way not yet recorded.

That does not question yet the idea that those architectures are essentially related to a Neolithic cosmogony. Structural transitions are just like that, presenting punctual and exceptional late extensions. So let’s see what the absolute chronology says.

One thing is already certain: this site is important to the problematics regarding Portuguese ditched enclosures.     

Valera, A.C (in press) “Mind the gap: Neolithic and Chalcolithic enclosures of South Portugal” (A. Gibson & J. Leary, eds), ENCLOSING THE NEOLITHIC: RECENT STUDIES IN BRITAIN AND EUROPE, BAR.