Company Logo

SBRG logo

SBRG office



Warning to the readers

Archaeoacoustic research in Portugal by SBRG

Taga: archaeoacoustics, archaeo-acoustics, Almendres, Escoural, Portela de Modos, low frequencies, rock art, infra-sound, ultrasounds, SBRG, SB Research Group

At the end of September 2014 some members of the SBRG travelled to Portugal in the area of Evora for an archaeoacoustic study on some Palaeolithic and Neolithic sites. Our work was requested by the invitation of the Portuguese archaeologist Fernando Coimbra with whom our group has already shared an archaeoacoustic research expedition in the Hal Saflieni Hypogeum (Malta) in early 2014.

It was not necessary to move around a lot in this area given the incredible concentration of dolmens and stone circles in this one location. Almost all of these sites are in extraordinary conditions and thanks to the cooperation of the local authorities, we were able to  investigate a range of less crowded sites to the better known ones.

However, after a week of full-time work, including a number of surveys carried out during the night, it was only possible to carry out, with substantial effort, on a thorough analysis of a few sites, although we visited, for a quick inspection, many prehistoric or protohistoric archaeological sites. Other areas of interest at this location will eventually be examined in a later mission if the laboratory analysis of the current recordings reveal interesting results.

Thanks to the availability of the area manager of Evora heritage, amongst the list of investigated sites we studied only at one Paleolithic site, the Escoural caves, we were able to perform an accurate analysis nestled among many rock paintings on the cave walls since immemorial time. This opportunity offered to our team enabled us to identify with the place, which, we have to admit, was definitely very impressive.


Fig. 1 - The Escoural caves in the path open to the public


The Escoural cave has been inhabited since the Middle Palaeolithic, i.e. between 100,000 and 50,000 BCE (Before Current Era), and was used as a shelter by Neanderthal man. However, it was also painted by more advanced men in the Middle Paleolithic period, which was is between 30,000 and 10,000 BCE, with geometric figures representing animals.

In the following images you can see pictures of an antelope shot by the forensic camera compared with the images obtained by a normal digital camera, but with resident program to increase the contrast of the photographed subject


Fig. 2 - The Escoural Caves: a beautiful antelope drawn by an artist who lived in the Middle Paleolithic painted close to the entrance of the main hall. Above: image captured with a camera sensitive to infra-red forensics. Below: the same picture, but taken with a digital camera with resident program to increase the contrast  


In the cave there are also some carved geometrical signs made by those ancient communities that lived here thousands of years ago. It is fascinating to think that while they were covered with dust for such a lot of time, the signs of their past existence is are still present.


Fig. 3 - Geometric petroglyphs on a wall of the Escural Caves in the deeper portions of the main room. The photo was taken by infra-red camera


The acoustic surveys in this area, highlighted the lack of resonance and using the compressor sound device for ultrasound (Pettersson D1000X), it was only possible to record the chatter of some bats bothered by our presence, however with the digital recorder we identified a very powerful frequency in the band of inaudible infra-sound.


Fig. 4 - Our surveys conducted in the Escoural Caves


In particular, there is an infrasonic frequency around 12 Hz due to the movement of underground water that seems to dominate many of the prehistoric sites in this region of Portugal.


Fig. 5 - The peak of natural infra-sound. recorded in the silence of the cave


In fact, thanks to the air column inside the cave that acts as a sounding board we can assume that this powerful frequency has also had an effect on the people who lived inside there in the past. Personally, after some hours living in this cavity it can be said that even some of us have, so to speak, been influenced.

Our research was then extended to the more well-known site of the cromlech of Almendres, where we verified if there was a presence of a significant resonance effect at the center of the larger stone circle between megalith 64 and 65 using a percussion instrument. Below is a map of the stone circle.



Fig. 6 - Map of the Cromlech of the Almendres above is visible the larger circle, the lower circle, the smaller circle, however, would seem to be that even the oldest (we are grateful for the map to the Portughese archaeologist Pedro Alvim)


At this site we made a number of sound and photographic surveys at different times of the day and night. The impression of this archaeological site is amazing, especially the light at sunset.


Fig. 7 - The Cromlech of the Almendres at sunset (photo: Nina Earl)


As in other megalithic sites in Europe, we performed a survey of infrasonic sound waves coming from the basement of tectonic origin or caused by the movement of groundwater. For Almendres, particularly in the smaller stone circle, we found infra-sound that were around a frequency of 7-8Hz, similar to what is found in the acropolis of Alatri (Frosinonone - Italy). As occurred in this site, these type of frequencies, have a strong relaxation effect on the human body and the ability to heal from stress. It can therefore be assumed that smaller stone circle of Almendres may have also had a thaumaturgical function.


Fig. 8 - Above: the peak frequencies around 7-8Hz verified by us within the stone circle at lower Almendres. Below: the position of the microphones placed at the center of the stone circle at the time of registration


 Fig. 9 - Panoramic image of the larger stone circle in Almendres(click image to zoom)


An interesting fact is that the granite megaliths emit ultrasounds when hit by sunlight, as revealed by the Pettersson equipment. It's is a phenomenon already discovered by British researcher Don Robbins of the Project Dragon Research Group in the 1970's years in Oxfordshire (U.K.) at the site of Rollright Stones Circle; a stone circle located in the South of England (Ref. "Circle of Silence", London, 1985). Thanks to our more sophisticated equipment, compared to that used more than 30 years ago, we discovered that the sun does not produce ultrasound, but rather the heat of the sun when it hits the granite megaliths does. It's is also quite logical because it's is solar energy heating up the stone that changes the motion of the electrons that pass from one orbit to another which causes this effect.



Fig. 10 - Some striking images of the megaliths of Almendres caught after sunset


This is particularly evident since the ultrasound emission continues even after the sun has gone is down and the stone is still hot. In the case of Almendres we verified that the sound is equally powerful for more than one hour after sunset. In the same way if the sun is blocked or shines from a short time the stone must first eliminate the cold and possible moisture accumulated during the night before the effect can be further observed.

We decided to call this phenomenon with the suggestive name of "singing" of the megaliths, because in ideal conditions it really develops a frequency very close to that which is audible. It is also possible that in ancient times the population living without the presence of noise of modern civilization, without a hearing volume deterioration from various machine tools or transportation, without the noise of loud music and in perfect harmony or connection with nature, they could possibly have felt this vibration. Especially when it came to people of  young age and with an auditory organ in perfect condition.


Fig. 11 - The research for sources of ultrasound in the cromlech of Almendres by Pettersson D1000X device


Our hypothesis were based specifically on Almeadres where the granite megaliths were shaped with a flat side facing toward the centre of the stone circle, almost like an old loud speaker with the side curved outward. The structural composition appears to have a double function, one, reflecting the sound of a source placed at the centre of the cromlech and two, allow those who are placed at the centre of the stone circle to perceive the "song" of the stones when hit by the sun. The effect would be especially interesting when the megaliths were correctly positioned, not like now that they have been largely moved or oriented differently from their original location. But we must also remember that they have almost been 8000 years at their current location.


Fig. 12 - The research team that conducted the research is FROM archeoacustica Almendres. From left to right: Nina Earl, scientific assistant, Paolo Debertolis, physical anthropologist, Fernando Coimbra, archaeologist


The same phenomenon was also found in the megalithic site of Portela de Mogos, a very little known, but very well preserved cromlech that has given us a lot of data for backing up our hypothesis.


Fig. 13 - A panoramic image of the megalithic site of Portela de Mogos (click image to zoom)


This stone circle is still surrounded by a forest of oaks and was discovered in 1966, but has been excavated and restored in its entirety as early as 1995. Its layout is shaped like a star and various megaliths have a flat face, carved by its builders. On some of them there are also engravings with lunar and solar motifs.


Fig. 14 - The good state of conservation of Portela de Modos stone circle



 Fig. 15 - The research for ultrasounds at the megaliths of Portela de Modos


We also conducted the archaeacoustic surveys at the standing stones of Almendres at a certain distance from the stone circle of the same name, but correctly oriented in the equinoxes with the corresponding cromlech.


Fig. 16 - The menhir of Almendres (click image to zoom)


 Fig. 17 - The menhir of Almendres during measurements


There have also been surveys undertaken at some dolmens of which we have yet to assess the implications from the point of view of the local natural acoustic phenomena. Unfortunately, some dolmens were transformed into Catholic churches in the sixteenth century, misrepresenting the function and changing the original plans.



Fig. 18 - An ancient dolmens converted to a chapel at the time of the Inquisition (Chapel Anta do San Brissos)


In particular, we focused on the famous dolmen Anta Grande do Zambujeiro, one of the largest in the world with dolmen stones that make up the architecture of the weight of several tons. This site is dated at the beginning of the 4th millennium BCE and unfortunately was uncovered with the capstone thrown some distance from the monument (see map below). Although there's now is an artificial covering built by archaeologists it is still possible to verify the presence of resonance phenomena in its interior.



Fig. 19 – Map of Anta Grande do Zambujeiro dolmen. Key: A burial chamber, B removed cover monolith of dolmen, C shot down menhir (courtesy of Portuguese Heritage Service)


 Fig. 20 - The megalith that served as a cover (point B on the map) of Anta Grande do Zambujeiro dolmen thrown farther and now broken



Fig. 21 - The access corridor to the dolmen and coverage by Portuguese archaeologists put there  to protect the structure


Fig. 22 - The main room of the dolmen view from the top (point A on the map)


This dolmen has an access corridor to the central chamber that is no longer used by the public. For these reasons, the microphones were lowered down by us.


Fig. 23 - It was not possible to access the main chamber of the dolmen with microphones, except through the opening top, with the cables falling



We also carried out tests with infra-red and ultraviolet camera with different types of light at different angles on some engravings carved on megaliths of Almendres (rock art). The results were exciting and will be presented next year in Caceres Congress (Spain) at the end of August 2015.


 Fig. 24 - Stone n. 65 of the standing stone circle of Almendres and how it looks during the day highlighting its carvings during the night with a high concentration of light and the use of a forensic camera. Finally, the complete design of the incisions present on its surface (courtesy of Portuguese Heritage Service)


Given the extensive collaboration with the local authority and the interesting discoveries on archeoacoustics, another mission is planned next year with a date yet to be determined.

Paolo Debertolis – October 30, 2014



Special thanks from SB Research Group to the Director of Heritage Service of Evora area, Antonio Carlos Silva, for his kindness and availability for supporting our research.


Edited by Pier Bond


Login Form


Powered by Joomla!®. Designed by: joomla 1.7 templates hosting Valid XHTML and CSS.

Copyright © 2024 SB Research Group. All Rights Reserved.
Joomla! is Free Software released under the GNU General Public License.