Rock niches in the Eastern Rhodopes
Rock niches are the most numerous group of megalithic rock monuments. Their distribution is mainly limited to the Eastern Rhodopes, especially in their central part. They occur along the middle reaches of the Arda River, together with the catchment areas of its tributaries - the Borovitsa, Perpereshka, Vrbitsa and Krumovitsa rivers, as well as along the upper reaches of the Olu Dere. They are usually carved in suitable rocks - volcanic tuff, less often sandstone, sometimes but less often in limestone or hard rock. They are usually carved on vertical cliffs, on prominent rock faces, often at a considerable height, and may be singly or in groups, usually on the sunny side of the cliffs (facing south, though there are exceptions).
Most often the niches have curved, expanding chambers, a vertical opening and a flat bottom. Their height varies between 0.60 and 1.00 m, depth about 0.40 - 0.45 m, base width is 0.30 - 0.50 m, and 0.20 - 0.40 m at the top. Almost all the larger complexes include several structures, the most common having trapezoidal openings, but some are rectangular or oval in shape, probably due to erosion.
The unfinished niches give an idea of the technology of their construction. Usually, the entrance (the trapezoidal frame) is sketched first, then the space is cut from top to bottom, and finally the walls are smoothed (it is likely that iron tools were not used for the cutting, but stone and bone-tipped tools). Cutting at a height of over 50 m required considerable skill and safe equipment.
Typically, from 3 to over 100 niches are carved into a given rock, with occasional single ones. As of 2021, over 4,200 individual units have been located.
The largest concentration is in the Gluhite Kamani complex (where there are 459 niches on an area of 0.25 sq. m. During the research, the team registered several rings carved into the rock, which are assumed to have served as a suspension for ropes that assisted in the cutting of the niches). The rock niche complexes near the villages of Angel Voivoda, Nochevo, Zhenda, Dazhdovnitsa, Bezvodno, Sarnitsa, Lisitsite, Chukovo, Chomakovo, Raven, Moryantsi, Efrem, Oreshari, Krasino, Skalina, Shiroko Pole, Dolno Cherkovishte, Ardino are especially numerous. Distribution in the west to the line Ardino - Bezvodno - Murga - Yonchevo, in the north the border reaches Dragoynovski Rid - Tatarevo - Dolno Cherkovishte - Malko Gradishte, in the south and east the border is difficult to determine, because there is a lack of complete information, but generally the eastern border is considered to be Kralimarkov Kamak in the Kovan Kaya area - south of Mezek, and the southern border is the northern slopes of the Maglenik Rid near the villages of Chernichevo and Gugutka.
Most scholars agree on their cult function and their connection with Thracian funerary beliefs, as well as with solar and rock cults. The most common interpretation is that they are associated with Thracian funerary rituals (the niches have similarities with the entrances of trapezoidal tombs, as well as with the entrances of cult facilities). Some scholars believe that the niches were used by the Thracian aristocracy, while others believe that they served as urns for ordinary people, formal necropolises. There are also alternative hypotheses that the niches are one-time ritual actions related to calendar days or a dedication ritual. According to others, they symbolize doors to the afterlife. Some scholars associate them with the cult of the Great Goddess - Mother.
