[3][4] Alternative explanations suggest the connection to the ancient mountain-dwelling Slavic pagan deity Kozmaj/Kasmaj, the protector of woods, animals and the cosmos.

The mountain is 5.5 kilometres (3.4 mi) kilometers long and built of flysch, serpentine, and magmatic rocks.

Until 600,000 years ago, when the surrounding low areas were flooded by the inner Pannonian Sea, the Kosmaj was an island, just as the neighboring mountains (Avala, Fruška Gora to the north, etc.

Moreover, during the excavation, a hidden entry into the vast complex of Roman mines was discovered, too, being obscured for centuries.

In the 1970s and 1980s, experts from the National Museum in Belgrade explored the area and discovered many mining necropolis, centered around the villages of Babe, Stojnik and Guberevac.

[7] In February 2022, it was announced that the Serbia Zijin Bor Copper company has been surveying the mountain for possible mining.

[10] Together with the Avala, the island of Veliko Ratno Ostrvo and the wood of Stepin Lug (and with forests of Košutnjak and Topčider to be added soon), the Kosmaj is a part of the circle of the protected green areas of Belgrade.

[11] The Kosmaj remained highly forested, over 70%, mostly by the deciduous (beech and oak), and to the lesser extent, coniferous woods.

While the beech and oak forests are results of the natural, spontaneous growth, the patches of conifers were planted by humans.

Self-grown plants used for human consumption include bear's garlic, woodland strawberry, blackberry and cornelian cherry.

[12] Altogether, 551 plant and 300 fungi species inhabits the mountain, including the endangered larkspur (Delphinium phissum)[13] which is on the Red List.

[14] Animals inhabiting the mountain include 13 amphibian, 11 reptilian, 51 mammal and 96 bird species, including the more common hares, roes, pheasants, foxes, squirrels, hedgehogs,[4] partridges and quails but also in Serbia rare, Red Listed corn crake.

Protected area covers 3.5145 hectares (8.685 acres) and spreads in the municipalities of Mladenovac (villages Amerić, Koračica and Velika Ivanča) and Sopot (Rogača and Nemenikuće).

Proximity of Belgrade and mountain's gentle slopes, glades and woods are a basis for the touristic economy.

There are also lake and hunting ground Trešnja and public swimming pools "Verona" in Rogača and "Izvor" in Stojnik.

Apart from the monasteries ("Mount Athos of Despot Stefan Lazarević"), touristic objects on the mountain include the Sopot Khan and the Old Žujović House [sr].

Numerous annual festivals are organized in the villages, dedicated, among other, to frula, fiacres, goulash or health food.

Historically, or in folk mythology, they are all in some way connected to the ruler Stefan Lazarević (1377-1427), who died while crossing the mountain.

With the Church of Saint Apostles Peter and Paul in the village of Nemenikuće, Church of Saint Elijah with Stefan Lazarević's cenotaph and several other objects, the Kosmaj's religious and memorial complex is colloquially called "Kosmaj's Mount Athos", a usual moniker in Serbia when a number of religious objects is clustered on one location.

Serbian Orthodox Church officially adopted 1417 as the construction year and in July and August 2017 celebrated monastery's 600th anniversary.

In the vicinity of the monastery are remains of the Roman cemetery, and the area was the favorite hunting ground of despot Stefan.

The central object in the complex is the church with the square based narthex, which can be classified as the representative of the Morava architectural school.

Construction of the new konak, planned before the war, began in 1991 and the foundation stone, brought from the Mount Athos, was placed by Princess Elizabeth of Yugoslavia.

[20][21][23] Tresije became somewhat of a sensation after the local population started claims that the image of Mary, mother of Jesus began to appear on church's outer wall.