The air hangs heavy, thick with incense. Candles litter the ground. Bare-chested men, glistening with sweat, huddle together. Ethereal shrieks ring out. Women, their eyes closed, their faces taut, suck deeply on cigars. A wizened shaman, a red bandanna around his head, clutches the neck of a beautiful girl, his knife poised midair, ready to strike. Men and women lie entwined, their bodies dusted with flowers.

This is Sorte mountain in northwest Venezuela, home to the mysterious cult of Maria Lionza, a syncretic, deeply religious movement that combines spirit possession, black magic, esoteric rites and Catholic rituals. Over three years, the Spanish photographer Cristina Garcia Rodero made many trips to the region to study the cult and its followers. Her images document the often disturbing reality of Venezuela’s unique faith.

The cult dates back to the 14th century, when indigenous tribes inhabited the foothills of Sorte in Yaracuy state, a lush mountain region 200 kilometres west of modern-day Caracas. At its cultural heart is the eponymous Maria Lionza, once the daughter of a powerful tribal elder, now a spiritual queen. Historical details are sketchy, but she was apparently an enchanting woman with striking green eyes. Legend has it she was kidnapped by a love-struck anaconda, who swept her away to a bottomless lagoon. There, she transformed herself into a goddess and ruler over all nature. The religion she inspired in Venezuela has evolved over centuries, embracing many different influences. First it was the Spaniards, led by Christopher Columbus in the 15th century, introducing devout Catholicism. Next, 17th-century slaves from West Africa opened the cult up to voodoo, paganism and black magic. In the early 1900s, settlers from Cuba and Haiti brought teachings from the Afro-American religion of Santeria. And in the 20th century, Venezuelan political leaders, including Hugo Chavez, have also associated themselves with the cult.

Today, estimates suggest around 30% of the Venezuelan population belong to the cult. It permeates through the social strata: doctors and high-ranking professionals worship alongside illiterate peasant families from city slums. The influence of Maria Lionza has even seeped out into Colombia, Brazil and Puerto Rico.

Political authorities in Venezuela have always respected the cult, even if its standing in this deeply conservative Catholic country has at times been uneasy. In Caracas, the capital, a 23ft statue of Maria Lionza, naked astride a tapir, stands in the middle of a motorway. Installed in 1953 on the orders of the dictator General Marcos Perez Gimenez, it broke on June 6, 2004, splitting at the waist and falling backwards to face the sky, just days after Chavez was successfully challenged in parliament by his political opponents. At the time, many Venezuelans felt that the goddess had deliberately broken herself in two, warning her people against the dangers of their divided nation.

The area around Sorte mountain, where pilgrims gather, was turned into a protected national park in 1960. Devotees believe important spirits inhabit the region. Many are key figures from Venezuelan history, including Simon Bolivar, the leader of the Independence movement, and Dr Jose Gregorio Hernandez, a beloved Venezuelan physician who died in 1919. Pilgrims ask the spirits for guidance, spiritual blessing and protection against misfortune.

Cult followers travel to Sorte throughout the year, but October 12 is the most important date, a public holiday celebrating the day in 1493 when Columbus first arrived in Venezuela. Throughout October, pilgrims travel to the mountain in groups; children, accompanying their parents, are initiated into the cult from a very early age. Followers carry candles and chalk, alcohol and tobacco, crucifixes, and animals – usually chickens – for sacrifice. Men go bare-chested, women wear shorts and vests. Both sexes wear special necklaces to ward off evil spirits. Clothing must be red, blue or yellow, representing the colours of the national flag. Followers believe spirits dwell in both the earth and the sky. To ease a spirit’s journey into the material realm, pilgrims remove physical barriers between themselves and the spirit world, taking off their shoes and ensuring rituals take place on natural surfaces. Throughout the October festivals, chalk drawings – depicting flowers and pagan symbols – decorate the mountainside, to evoke communication with the spirits.

“The whole scene is overpowering,” says Dr Barbara Placido, who wrote her Cambridge University PhD on the cult. “Because interaction between spirits and humans takes place at night, an incredible sense of anticipation builds throughout the day. People burn incense, cook, sing, dance, shout and scream. The way each medium communicates with the spirits varies greatly, depending on what kind of guidance is sought by their pilgrims.”

Mediums work in pairs, a partnership allowing one, the materia, to become possessed, while the other, the bonco, deciphers the spirit’s message. Once possessed, mediums act as they please, liberated from the normal social taboos in Venezuelan society. Mediums spit and swear, smoke and drink and often strip naked. Some engage in self-mutilation, goring themselves on blades and glass, but always take care not to harm any pilgrims under their counsel.

“Maria Lionza was taboo in Venezuela for a long time,” says Marianna Ferrara, a Venezuelan documentary-maker. “It was always viewed with a lot of stigma, but attitudes changed. In the 1950s, word of the cult reached the artistic community in Caracas, then spread to the middle classes. Ruben Blades, a popular Latin-American singer, wrote a song about her in 1977. The cult gets much more attention now; the number of followers is definitely on the rise.”