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Archaeoacoustic research in Bogumili’s Dolina in the North-East of Italy

Tag: dolmen, menhir, dollina, Bogumili, archaeo-acoustics, archaeoacoustics, archaeology, SBRG, SB Research Group

In May 2014 SBRG began to examine a possible Neolithic site located on the Slovenia border called Dolina of Bogumili.

A “dolina” is a subsidence on the surface triggered by the collapse of an underground tunnel which has an underground river runnning through. It is caused by the process of "karstification", the chemical dissolution of calcareous rocks. The corrosion occurs by work of meteoric water that containins a certain amount of dissolved atmospheric carbon dioxide, when falling on the soil above ground CO2 is deposited.

This process creates the formation of long-distance underground tunnels, when they collapse they can sometimes create a sinkhole, a deep depression in the ground roughly circular in shape.

At Dolina of Bogumili, the depression in the ground has been used from time immemorial to build a type of amphitheater which features some superb acoustic characteristics. On one side at the bottom of the surface depression, there is a dolmen with a narrow entrance passage leading to a round chamber at the end which is covered by soil. In some aspects it has similar features to the Tombs of the Giants in Sardinia.

In the following pictures you can see the abandoned state of the amphitheatre, highlighted and circled in red is the entrance to the dolmen.



Fig. 1 - The Dolina of Bogumili: highlighted in red the entrance of the dolmen on the bottom of the depression


 Fig. 2 - The entrance to the dolmen. In the foreground the anthropologist Alessandro Severi who has previously collaborated with SBRG group in Bosnia and Herzegovina


Fig. 3 - The long, narrow corridor leading to the round chamber at the end. Everything is built with large dry stones and covered by earth


As you can see from above pictures, the structure was entirely built of dry stone, then covered with earth.

As in other sites we examined using our archaeoacoustic standard (SBSA), we used a shamanic drum (similar to an "Irish" Bodhrán drum) outside the megalithic structure then recorded the harmonics produced.

 Fig. 4 - We recorded the harmonics from a shamanic drum played in the site over the dolmen as the base line of the sound inside the depression of the surface (“dolina”)


We found that by positioning the shamanic drum at the entrance to the round chamber, it was possible to create resonance throughout the dolina with three specific frequencies which were different from the base frequency of the drum and its harmonics.

It is not known when this dolmen was built, but the menhirs scattered within the valley suggest a prehistoric period. The first traces of documentation dates back to 1600, oral tradition tells of the bugomilic heresy using it in the Middle Ages. Usually bugomili did not build these structures, as they made use of those structure already in existence. Some excavations carried in this site discovered shards of Roman dishes, so it can be assumed that the structure was in existence before the Middle Ages.

The images of some of the megalithic menhirs scattered within the dolina.

Fig. 5 - There are many menhirs scattered at different levels in the depression of soil


Some local historians have speculated this site was a Celtic tribunal with an audience sitting on the stands. This theory is hard to accept, if there was an audience, they would have had to stand up. In fact, the steps are too high to support sitting and if that happened, people would of had to tip their legs and with the sharp edge of the stones it would have been very comfortable. The appearance is clearly prehistoric, so its origin goes backdated respect the official dating, also because the archaeoacoustic characteristics found in this first investigation were common in several prehistoric temples we analyzed in previous missions in Europe.

This site presents an ongoing archaeoacoustic challenge for our research group. The volume and timbre of the drum changes substantially in the amphitheatre, when you turn on the resonance going to place the drum between the dome-shaped room, inside the dolmen, and the entry corridor. That is, the dome serves as a sound box and vibrates the entire amphitheatre when the drum is placed in the "node" of resonance. It was possible to detect this both graphically and directly by the microphones placed in or outside of the dolmen.


  Fig. 6 - The noise characteristics of the shamanic drum outside the dolmen. It’s clear a base frequency of 71Hz from which then departs its harmonics


 Fig. 7 - The Analysis of sound that propagates inside the dolina when the drum is played inside the room. The sound of the instrument is filtered and only three frequencies come outside, these correspond to the resonant frequencies of the rounded room in the central dolmen


Here you can find a sample sound file recorded in the valley during the experiment (about 17 per second you can feel the difference in the sound when you turn on the resonance).

This phenomenon is not to be considered by pure chance, the whole structure would seem to have a ritual function based on its acoustical effect.

As proof of what we have just said you can compare what we found in another room placed inside  the middle of the tiers of the amphitheatre. This room, well integrated into the overall complex of the amphitheater, though built with the same method of the dolmen, is totally devoid of sonic characteristics that make it a simple shelter, also equipped with louvers that illuminate the interior.


Fig. 8 - The second room present at a level higher than the side of the valley and steps (circled in red the entry). The photo is taken from the bottom of the surface depression (dolina)


 Fig. 9 - Detail of the entrance of the room-shelter


Fig. 10 - The loopholes in the room-shelter locations inside and outside. This room is completely devoid of sound properties


The dome chamber is situated centrally inside the dolmen at the end of a corridor, it is dark inside as there's is no natural light. It is similar in many respects to so called megalithic 'mound tombs', such as Newgrange in Ireland, all be it on a much smaller scale.


Fig. 11 - The long corridor of Newgrange, which leads to a central round chamber. Design by William Frederick Wakeman, 1900


Fig. 12 - For the evaluation of the sound characteristics of the round chamber, we placed the microphones both at the end of the long corridor inside the structure and at its entrance


Fig. 13 - For all other archaeoacoustic assessments the microphones were placed at the center of the sinkhole


Among other acoustic characteristics detected, there is also a low-frequency continuously detectable here and partly around the dolina. Probably this originates from underground movements of water, but justify the choice of ancient people for building a temple in this depression of soil, just like many other Neolithic temples we examined.
The archaeoacoustic research on this site will continue in the coming months.

Paolo Debertolis, Nina Earl – July 7, 2014




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