Excavations at Bolores

Bolores is a small artificial cave that housed the remains of at least 36 people who died between 4800 and 3800 years ago. Bolores faces the east, overlooks the Sizandro River, and extends approximately 5 meters north-south and 3 meters east-west. People in the ancient past selected this natural sandstone outcrop for their dead and then modified it to best accommodate their needs. They carved into it, excavated into the shale bedrock to create a basin, and brought in large sandstone boulders from the surrounding countrywide to divide up the space into three chambers.

Plan of Bolores
Plan of Bolores

Because Bolores was a culturally modified space, it is considered to be a ‘semi-artificial cave.’ These kinds of burial sites were one of many different locations in which the dead were housed in ancient Iberia. The dead were also buried in natural caves and rockshelters, megaliths, or corbel-vaulted tombs (known as tholoi). There was a lot of diversity in burial structures in ancient Iberia.

What do you think this diversity tells us about ancient Iberians’ ideas about life and death?


Excavating Bolores, 2010
Excavating Bolores, 2010

Bolores was excavated during four field seasons (2007, 2008, 2010, and 2012) by an interdisciplinary team directed by Katina Lillios and Joe Alan Artz at the University of Iowa, with Anna Waterman as project biological anthropologist. The Bolores project was one component of the Sizandro-Alcabrichel Research Project, initiated in 2007 by Katina Lillios and Michael Kunst (German Archaeological Institute, Madrid) to better understand the history of human lifeways during the Copper and Bronze Ages of this region.

Eating lunch at A Conchinha with the crew of the Zambujal excavations, directed by Michael Kunst (left, blue plaid shirt)
Eating lunch at A Conchinha with the crew of the Zambujal excavations, directed by Michael Kunst (left, blue plaid shirt), 2007

Who paid for this research? In part, Americans paid for this project through their taxes, some of which go to the National Science Foundation, which awarded us a grant between 2012-2016. These funds paid the travel expenses of key project personnel to get to Portugal for fieldwork and for them to present their work at conferences, provided a stipend for students participating in the project, covered the salaries of the many collaborators and students who carried out analyses and prepared maps and photographs, and paid for equipment and supplies. In the early stage of the project, support was also provided by a grant from the University of Iowa. The municipality of Torres Vedras also helped our project by paying for the lunches of our crew. We are very grateful to all these institutions.

Bolores was known to Portuguese historians as an ancient burial site since the 19th century, although it was first brought to the attention of archaeologists in 1986. At that time, local landowners were constructing terraces for vineyards near Bolores, and these activities exposed archaeological materials from the site. A two-week excavation in 1986 followed. The materials recovered from this testing confirmed a Late Neolithic/Copper Age date for Bolores. Although archaeologists sometimes discover sites, very often they learn about them from people living in the area.

Are you aware of archaeological sites near your home or community? Are these sites known to archaeologists? Do you know where your State Archaeologist is? This website will help you find them.  

During the fourth and third millennium BCE on the Iberian Peninsula (as throughout western Europe), people placed their dead in caves, rockshelters, artificial caves, megalithic monuments, or corbelled structures. These burials typically housed many people, which is why we call them collective burials. During this time, burials were also located some distance away from settlement areas. What this means is that people had to transport their dead, sometimes kilometers, to be buried.

How do you think they did this? What would these processions have been like? Remember, there were no hearses at this time. 

Recording the location of a bone before removing it
Anna Waterman (center) recording the location of a bone before removal, with the help of Ana-Monica Racila (left) and Jess Beck (right), 2012

One of the challenges of excavating and interpreting collective burials is that the bones are often very mixed up and fragmented. To make sense of collective burials, like Bolores, archaeologists work hard to dig carefully and record the precise location of each fragment. We used a total station, photographs, sketches, and notes to record the location of each fragment. We excavated using paintbrushes and bamboo skewers to make sure we didn’t damage the bones. The work was slow-going, but in the end, we were able to produce detailed maps, which helped us to interpret how the bodies were laid out and later moved.

Michael Kunst (left), director of Zambujal excavations, showing Bolores crew members one of the towers at Zambujal
Michael Kunst (left), director of Zambujal excavations, showing Bolores crew members one of the towers at Zambujal, 2007

Bolores was used as a burial over the same time period that people lived at the nearby settlement of Zambujal, 2 km away. We know this because we obtained radiocarbon dates from 11 individuals buried at Bolores, from different areas of the site and different depths. A child buried at the site was dated to 1800 BCE, indicating that a memory of the site as a burial endured some 700 years after its original use. Given the relatively short span of time that Bolores was used for, it could not provide information about the impact of environmental change on the lives and health of the people buried at the site. For this reason, we turned to a study of the animal bones found at Zambujal, which you can read more about here.

At Bolores, the skeletal remains of at least 36 individuals were found. Of these, nineteen were adults, four were adolescents, and thirteen were children. Both females and males were identified. The active lives of these farming peoples caused significant wear and tear to their bodies. The work of Jennifer Mack showed that many had arthritis. You can learn more about the diseases and pathologies of the Bolores people here:

For her honor’s thesis, Ana-Monica Racila carried out a radiogrammetric study and determined that they had strong bones, the result of a lot of physical labor. Their diet must have included coarse grains, which led to significant dental attrition (wear on the teeth). There was a high rate of childhood mortality. Given the relative lack of evidence for prolonged illness within the population, there appeared to have been more acute rather than chronic illness.

What kinds of stories would your bones tell about your life?

In studying the skeletal remains, it was possible to reconstruct the diet of these individuals. Anna Waterman coordinated these studies. The bone collagen, or fibrous tissue, reflected the sources of protein in their diet. Bone apatite, or hard tissue, reflects the whole diet. It appears their diet was based mostly on C3 plants, which include wheat, barley, legumes, and olives, and terrestrial animals. Children received less protein than adults. Some adults may have received additional protein from omnivores like pigs. There does not appear to be evidence for using aquatic resources as a major source of protein, which is odd considering the fact that there was an estuary located close to the site at that time.

Examining certain traits on the teeth of the dead found at Bolores indicated that some of the dead may have had ancestors from North Africa, according to collaborators Joel Irish and Briana Horwath. This would be in keeping with what we know about the trade network that brought North African objects, such as ivory and ostrich egg shells, to Iberia and as yet unknown items from Iberia to North Africa (although ceramics are a possibility). The biological evidence suggests, therefore, that people, as well as objects, moved across the Strait of Gibraltar.

The study of strontium isotopes (87Sr and 86Sr) in the bone and teeth of people (and animals) can tell archaeologists something about the mobility patterns of that person (or animal) during their life. Anna Waterman also coordinated these studies. Specifically, the ratios of strontium isotopes are compared to local geological signatures to determine whether the person (or animal) had moved from one geological zone to another in their life. Analyses of the strontium ratios of 19 of the 36 individuals found at Bolores revealed that they all appear to have spent their lives in the local geological region.

At Bolores, we found a series of limestone and sandstone slabs, roughly triangular in shape, positioned throughout the floor in a north-south line. Although both limestone and this particular kind of sandstone can be found nearby, the stones must have been brought to the site specifically for the ritual. Skeletal remains were found close to the slabs, though generally the bodies do not appear to have been placed directly on them. One possible use of the slabs is as pavements or thresholds that allowed people to walk through the tomb without stepping on the bones of their dead. Indeed, that is how the archaeologists used them during the excavation. The slabs may have also demarcated family groups.

Ochre staining on one of the slabs and surrounding bones
Ochre staining on one of the slabs and surrounding bones

Ochre was found on many bones and in the sediments. Ochre is a naturally occurring iron oxide used as a pigment by many ancient peoples, with a bright red or yellow color. A study by Lily Doershuk showed that about 7% of the bones found at Bolores were stained with red ochre, the majority in Zone II. Patellae (kneecaps), tarsals (foot bones), and carpals (hand bones) were the most common skeletal elements found with ochre staining, although it is possible they simply preserved the staining better. Ochre was also found both beneath and above some of the slabs, suggesting that the spreading of ochre was part of the burial ritual.

Some artifacts were found at Bolores, although they were less numerous than in most burials in the region. These objects included ceramic bowls, flint blades, a bone point, a bone handle, 23 stone and shell beads (read more about Jonathan T. Thomas’ PhD dissertation on the beads at Bolores and other sites in the region), and stone ‘idols’. An ‘idol’ is not a very specific term, and does not necessarily mean people were using these artifacts in a religious way. Rather, it refers to a unique object that archaeologists are not sure of its function. Only one complete ceramic vessel was recovered, which was a small bowl with bone fragments, ochre, and charcoal. The rest of the ceramics found at Bolores were small sherds.

Bolores bones leaving the University of Iowa to return to Portugal
Bolores bones leaving the University of Iowa to return to Portugal, 2014

Do archaeologists get to keep the things they find? They do not, normally. In the case of the Bolores finds, we were able to transport them to our laboratory at the University of Iowa for study. After our studies were complete, we shipped everything back to Portugal to the Museu Municipal Leonel Trindade, in Torres Vedras, where they are stored.

Quartzite bola
Quartzite bola


The stone ‘idols’ included a quartzite bola, a limestone mace, a limestone cylinder, and a calcite betyl. The bola and mace are both unusual finds for the time period. The bola, which has a pecked groove around its circumference, shows no signs of having been used as a hammer. The limestone mace has a hole at its bottom, which suggests it was mounted on a pole or stick. The limestone cylinder is similar to other such cylinder found in burials at this time in southern Iberia.

Calcite betyl
Calcite betyl

The calcite crystal is translucent and was polished. What is interesting is that these four objects were all found in the same area of the site, in Zone III. Perhaps they were used in healing or other rituals? Perhaps a shaman was buried in this area of the site. Archaeologists sometimes call objects ‘idols’ when they do not know their original function. What do you think they were? 

Also found in Zone III, along with the remains of adults and adolescents, was a child burial, underneath whose head was found a complete rabbit skeleton. It seems very likely that the rabbit was placed there as part of the child’s funeral. Rabbits are often found in burials of this time period in the Iberian Peninsula. Given the high percentage of child burials at Bolores, and at other sites of the time, childhood mortality must have been fairly high. Still, the deaths of these children were marked by rituals, and they were buried in a similar way as and alongside older members of their community. Does this surprise you? Why? 

It appears that the dead of Bolores were treated to several stages of processing following their initial internment. Liv Nilsson-Stutz conducted these studies, which are known as archaeothanatology. When bodies were first introduced into the cave, they were likely wrapped with either rope or cloth, and placed in a flexed position, sometimes face down or leaning on the side. Within each section of the cave, there was movement of the remains after some decomposition, but there was no movement from one section of the cave to the other. Except for one adult skeleton, all remains show signs of extensive post-depositional disturbance. The larger bones are often absent, perhaps a result of these larger elements being moved to make room for new internments. There is no apparent patterning by age or sex to the human remains by zone. In Zone III, we found a bone bundle, made up of bones from at least two individuals. Why do you think the bones from different individuals were grouped together in this way? 

Reconstruction of Bolores, from outside and inside. Paintings by Guida Casella

What did Bolores look like? When you see Bolores today it is very difficult to imagine what it might have looked like 4500 years ago. The roof of the rockshelter has collapsed, and there is little in the way of the tomb left behind, now that we have excavated the site almost in its entirety. For that reason, we worked with two Portuguese artists – Guida Casella and Leonel Trindade – to help us think about what it might have looked like. Guida created , and Leonel made a scale model. How did they come up with these images and model? Above all, they worked with information we had found from the excavations, including the size and shape of the tomb. We could also suggest, based on the fact that the human remains did not show any gnaw marks by scavenging animals, that the tomb must have been protected or enclosed. But there is a lot that was not preserved, such as the building material or where the entrance of the tomb was. Here we had to use our imagination a bit and consider what other contemporary tombs from the Iberian Peninsula looked like.

Leonel Trinidad with model of Bolores
Leonel Trinidad with model of Bolores

If you’re interested in learning more about Bolores, some of the publications listed here will provide additional information.

To hear a summary of the Bolores project, in English and in Portuguese, and see some more images, check out these videos: