BOGOTÁ — The Siona and the Quillacinga, two indigenous groups of southern Colombia that are fighting to protect their land and traditions from the depredations of the modern world, sealed their friendship with a sacred plant in the Amazon.

Six Siona elders and shamans called taitas recently made their way to a Quillacinga community at La Cocha, a lake located a chilly 2,600 meters above sea level in southern Colombia. They carried a plant with hallucinogenic properties called yagé (also known as "ayahuasca") in a school satchel as they steered a boat up the Putumayo river that flows toward the Brazilian Amazon.

About a decade ago, the Quillacinga people living around the La Concha lake decided to act against the steady decline of their traditions in the modern world, and found in the Siona an ally and collaborator. Both ethnic groups share the rainwater that feeds La Cocha lake, which trickles down the hills into the Putumayo river where the Siona sail and fish.

After a couple of hours on the river, the party arrived at a city close to Ecuador's border. From there, they took a bus. It was a slow trip and the Quillacinga waited patiently for their guests. Delayed by a mudslide, the Siona elders finally arrived at La Concha at nightfall. They were led to the house of Roberto, a Quillacinga farmer, who in 1998, decided to adopt the lifestyle of his ancestors and turned into a shaman.

The guests were driven along the lakeside to a nearby hamlet, El Romerillo, where 30 peasants awaited the start of a certain ceremony.

First Night

The Siona shamans wore sleeveless tunics and necklaces made of boar teeth and seeds. Exhaustion abandoned their faces as tobacco smoke, chants and prayers filled the house they had entered. The men were given a potion of the yagé plant in a small vessel ringed with specks of sugar to counter the plant's bitterness. They then retreated to sit on benches at the edge of the house. After them, it was the women's turn.

As the shamans chanted litanies, the only lit bulb is turned off and this seemed to enhance the sound. Two youngsters moved around with incense while those seated in the room, cloaked in ponchos, were still as rocks.

I was concerned: Why hadn't I brought a camera or a notebook? One of the Siona shamans, Sandro, told me the only picture I should take with me should be in my heart. I closed my eyes. When I opened them, everything around me seemed to have changed its consistency. The universe seemed to be made up of a different material. Time had stopped. I remember seeing the moon edge a little to the right, like a clock hand.

One poncho-clad youngster appeared to be in a bad dream. The others were still, each on their own trip. I felt warmth. My lost memories returned and I was reminded of all the decisions I had taken or would have to take. The experience the plant provoked was indescribable. Any attempt to use language to explain it is useless.

A tenuous, fuzzy sunrise suggested the night had ended and smiling faces emerged from the fog and cold. The experience had been a healing one. The village soon resumed its daily routines — women peeled potatoes, cooked, and attended a baptism at noon. A downpour began.

Second Night

That night the shamanic rite was repeated. It was a ceremony that is learned and passed on through generations, and perfected over centuries. The ancestors "are not the past," said one of the shamans, "because they are ahead in time. They have already moved on and we are the ones walking behind them."

Necklaces rattled and sounds of prayer and healing resumed. Incense filled the house. Men filed past the shamans and received a second shot of the "remedy." The women followed. Again, they disappeared into the night's darkness, each person alone and intoxicated with visions.

Sunday was a holiday in the hamlet. There was a barbecue of guinea pig and homemade wine. The Siona and Quillacinga sang all afternoon.

I was concerned that I hadn't jotted down or filmed any of the native rites. I wrote nothing about how and when the Siona and Quillacingas became friends. I seemed to be returning toEl Espectador empty-handed. But now, I understand, the experience could not be filmed. I had initially sought out the shamans to ask what they thought of mental illness and wellbeing in Colombia, about modern and traditional medicines and the government's health services. Their response had been to invite me to the ceremony, so unrelated to our medicine and culture.

The plant and ceremony were their "remedy," and I could see why. While our pharmaceutical products limit or alter neuronal activity to control psychotic states, this plant expands the user's view of life. Our treatments are personalized and selfish. This plant helps the Siona to remember fundamental values of life, which is a part of their defense against modernity's brutal advances. Everything we do, on the other hand, is to distract ourselves and avoid introspection.

The Siona started their trip home the next day laden with food and presents the Quillacinga had given them to thank them for sharing their remedy. Before they left, they told me an oil firm had arrived on their land. "There is no inner peace without peace with nature," said one of the shamans. But the Siona were not sad. They had suffered worse over the centuries and the plant would show them a way to overcome this ordeal too.

On April 21, Siona authorities issued a resolution explaining their opposition to seismic studies slated to be carried out on a strip of land inside the Buenavista reserve where they live. In keeping with the guarantees provided to them by Colombian laws, the Siona declared the whole reserve to be sacred.