Tag Archives: geophysics

Building 3

The geophysical survey carried out in the field to the west of the site revealed a building that clearly differed from its surroundings; this was identified as “Building 3”.

In 2017, it was decided to excavate in this location with the aim of characterising this construction with regard to both its structure and function. In addition, this excavation enabled us to document more of the settlement’s urban structure.

Since that first campaign, every summer this building has been the site of a dig that is used as part of the theoretical-practical course organised for students at Edinburgh University.

The excavation has, so far, led to the discovery of an almost rectangular building, measuring 8m x 11.5m. It has two rooms in the north and a large area on the southern side, which is still being excavated.

A great deal of material has been found in this building. It tells us about both the life of its inhabitants (pottery ware for drinking and eating, game pieces, coins, etc.), and about its end, as several charcoal deposits show that it caught fire. Among the rubble of the largest room, the first anatomically connected human remains from the settlement have been found.

Building 4: area 4

The geophysical survey carried out at the beginning of the project revealed, among other elements, part of the urban structure of the site. Building 4 was detected in the centre of the field. It is a large building (about 450m2), with a prominent “C” shaped room (area 4), which had apparently been burned.

The 2011 to 2013 campaigns focused on this area and demonstrated that it is a closed space, even though the east wall, which is narrower, deeper, and built with smaller stones, was not detected by the geophysical techniques. The only access to the area is on the south side.

The traces of fire were also corroborated during the excavations, as several burned beams were found, probably from an attic, which had fallen on several pottery pieces. One of the pottery pieces is a black-glazed krater from present-day Sicily, which was used to mix wine and water. The resulting liquid would have been consumed using cups, also ceramic, in this case imported from the Italian peninsula.

The presence of these elements denotes a certain level of luxury. This makes us suspect that the building could have played an important role in the settlement, although future work is needed to confirm this.

Panel 5. Puig Ciutat: A scientific and educational laboratory

Why is Puig Ciutat important?

The process of Romanisation in the Lluçanès region is still not fully understood. Nevertheless, the study of this archaeological site could spur new research into this historical period in Central Catalonia.

Since 2010, a team of researchers have performed various interventions on the Puig Ciutat site and its vicinity. These interventions were based on a multidisciplinary methodology which includes phases of surveying, excavation, treatment and publicising of the results.

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Surveying:

What does it consist of?

Reconnaissance and exploration of the archaeological area using satellite imagery, aerial photographs, topographical models, the search for surface remains (ceramics, metals, etc.) and geophysical methods.

What does it allow?

Detection, documentation and description of possible archaeological sites.

Planning of the excavation.

Excavation:

What does it consist of?

Excavating a particular terrain to locate clues and evidence of ancient societies.

What does it allow?

Recording and documentation of the remains discovered during fieldwork and the stratigraphic information obtained.

Interpretation:

What does it consist of?

Classifying, restoring, digitising and interpreting the archaeological material (ceramics, metals, fauna, etc.).

What does it allow?

Initiation of studies and formulation of hypotheses among specialists in Archaeological Science.

Dissemination:

What does it consist of?

Informing society about the research undertaken on the basis of the site, through reports, guided visits, congresses and media.

What does it allow?

Socialisation of scientific and cultural knowledge for all publics.

Panel 6. Puig Ciutat: Geophysical prospecting

What is geophysics and why is it applied in Puig Ciutat?

Geophysics is the science that applies non-invasive systems for exploring the subsoil. It was applied right from the start of the project as a tool that could help manage the excavations. Puig Ciutat is also an experimental site that enables us to test equipment and develop working methods. In addition to the surveys carried out in the early years, which are presented here, a systematic survey of each new area to be excavated is carried out at the beginning of each dig.

We are able to systematically apply geophysical techniques at Puig Ciutat thanks to the participation of the company SOT Prospecció Arqueològica.

Magnetic prospecting

What does it consist of? This measures local variations in the Earth’s magnetic field.

What does it enable us to do? It is useful for identifying kilns, hearths, burned areas, metals, filled trenches, as well as for delimiting sites.

Magnetic gradient map: burnt areas and possible metals are indicated in red, possible streets or ditches in white (data from SOT Propsecció Arqueológica)
Magnetic gradient map: burnt areas and possible metals are indicated in red, possible streets or ditches in white (data from SOT Propsecció Arqueológica)

Ground-penetrating radar (GPR) prospecting

What does it consist of? This measures variations in humidity by emitting an electromagnetic pulse, the echoes of which are subsequently received at the surface

What does it enable us to do? It is useful for detecting built structures, and allows us to visualise what structures are like at depth.

GPR reflectivity map: the built elements and bedrock are represented in black (data: SOT Propsecció Arqueológica)
GPR reflectivity map: the built elements and bedrock are represented in black (data: SOT Propsecció Arqueológica)

Electromagnetic prospecting

What does it consist of? This measures variations in conductivity and magnetic susceptibility by analysing the way the subsoil responds to an electromagnetic field applied from the surface.

What does it enable us to do? It is useful for characterising substrate composition and indirectly defining parameters like salinity, permeability, and porosity.

Electrical conductivity map: the black areas were interpreted as either the limey marl bedrock or construction material from the site; the white areas are clayey marls of the upper levels (data: Ghent University, Belgium)
Electrical conductivity map: the black areas were interpreted as either the limey marl bedrock or construction material from the site; the white areas are clayey marls of the upper levels (data: Ghent University, Belgium)

Interpretation of results

What does it consist of? This gives archaeological meaning to variations in the physical properties of the subsoil.

What does it enable us to do? This allows us to extract the archaeologically most significant elements from the geophysical images

Interpretation of the results: synthesis of the results and classification according to archaeological significance
Interpretation of the results: synthesis of the results and classification according to archaeological significance

Aerial and relief images: www.icgc.cat

Panel 7. Puig Ciutat: an unusual building

Archaeology, like any science, has its own methodology which is adapted according to the objectives and circumstances of each case being studied. In this respect, the work undertaken on the structures of the present building serve as an example to explain the scientific method applied in Puig Ciutat.

The present state of the excavations does not yet allow an answer to many of the questions hinging on the site. Nevertheless, geophysical surveying has made it possible to focus the excavation in those areas where the presence of built structures has been recorded. Thanks to this strategy, in a short time we have been able to obtain the largest possible quantity of data for drawing up the first interpretative hypotheses.

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Surveying:

What do we know?

Geophysical surveying has identified the presence of a building in the middle of the agricultural area. Some of the techniques used, such as ground-penetrating radar, have made it possible to define the geometry of the structure and establish its depth about 0.5 metres (20 inches) beneath the surface.

Excavation:

What do we see?

A building measuring 11 x 11 metres with an entrance in the form of a passageway which very probably opened onto a distribution space inside. Two rooms have also been made out abutting the main façade and, finally, a space subdivided into four compartments at the back. The two innermost rooms are of a smaller size.

In the course of the excavation, a large amount of carbon and shattered ceramics have been documented that suggest the building may have been destroyed.

Interpretation:

What do we deduce?

The building is an unusual construction that stands out in the settlement. Its size suggests it could be the residence of the commander or person in charge of the establishment praetorium) or a building with an important administrative function in the same context (principium).

Although at present the data do not offer any more information about its purpose or its destruction, we hope to obtain more results in future work.

Building 1

Aquest sondeig es va realitzar amb l’objectiu de confirmar la presència i les característiques d’un edifici de grans dimensions, que havia estat prèviament detectat per les prospeccions geofísiques.

The archaeological excavation revealed a square building, 11 by 11 metres, divided up into various rooms opening onto a central distribution space. This was reached by a passage that communicated with the building’s only entrance, open in the southern façade. The date provided by the ceramic material recovered confirmed that the building belonged to the latest phase of occupation of the settlement, in the Late Roman Republican Period.

The work revealed that the structure had been heavily affected by farming work in the field in recent times and some of the walls that divided up the complex have not survived. Despite the poor condition of the remains, carbon was found which could have been part of the door latch.

Two surveys performed in the interior of the building showed that it had been looted in ancient times, probably to recover some of the stones from the north and west walls.

Its large size make this building an important one in the settlement’s complex of buildings. According to documentary sources, a building of these characteristics could have been the praetorium, or residence of the Roman camp’s Commander, or the principia, or administrative building. In the case of Puig Ciutat, this building could have fulfilled both functions.

Geophysics

Geophysical methods have made it possible to explore the site in detail and more exactly define the geometry of the structures and their geological surroundings. In this context, geophysical surveying has centred on two fields in the western section and, especially, on the field in the eastern sector, as they allow extensive work that is impossible in the wooded areas.

The main techniques used are magnetic surveying, which provides information on areas with alterations in the electromagnetic field like the ones produced by combustion, ground-penetrating radar, which provides a more precise description of built structures, and electrical surveying, which documents variations in the potentials of sediments.

The results and interpretations obtained with the different techniques are used in the planning and management of subsequent excavations.

Image: © Orthophotograph property of the Institut Cartogràfic i Geològic de Catalunya, accessible on www.icgc.cat.

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The Local Context

A Game of Strategy

Puig Ciutat stands in a meander of the Gavarresa stream, which provides a natural defence along part of its perimeter but gives it little long-distance visibility. Occupation of this site, then, probably didn’t respond to the strategic advantages of this meander.

What did the inhabitants of Puig Ciutat defend or control? When was it destroyed? At the end of the Roman Republic? Where was it attacked from? What factions could assailants and besieged have belonged to?

As we’ve seen, some of these questions have now been answered thanks to the work carried out so far.

To solve these mysteries, the Puig Ciutat team is applying traditional archaeological exploration as well as geophysical archaeology or remote sensing over a large area surrounding the site.

Picture: © LIDAR data property of the Institut Cartogràfic i Geològic de Catalunya.