“As we sit in running water and listen to the voice of the cleric praying for us as he pours water on us, we keep alive the tradition of John the Baptist, the first baptist in history,” says Nariseh, 25. 

Nariseh has come to the Iranian capital Tehran to pursue her studies, but sometimes feels alone there as she belongs to the Mandaean minority, whose ancient faith is unfamiliar to most Iranians.

“There are many people in this city who have never heard of us,” she said. “Some regard us as star-worshippers because we have to face the North Star for prayer.”

Nariseh says she is in awe of the uniqueness of her faith.

“I sometimes find myself in a bustling world in which the people of different faiths and ethnicities have intermingled, and yet I am a follower of an ancient tradition that traces my lineage back to Adam,” she said. “This makes me determined to safeguard my Mandaean identity.”

The Mandaeans, or Sabians as they are often known, are followers of John the Baptist, but are not Christians. They say they are descended from Noah’s son Shem, and thus from Adam.

Abu Rayhan Biruni, the 11th century Persian polymath, argued that Mandaeans represented “the remnants of Jewish tribes that remained in Babylonia after the other tribes left for Jerusalem”, after Iranian monarch Cyrus the Great captured Babylon and liberated the Jews there from captivity.

A more commonly accepted narrative among the Mandaeans is that they originated on the River Jordan and left there to follow John the Baptist, eventually finding refuge in present-day Iraq and Iran.

Islamic tradition accords the Mandaeans the same special status as Jews and Christians as “people of the book”, in other words the common Biblical foundations shared by Muslims.

Because the act of baptism is central to their faith, Mandaeans have historically settled along rivers – the Tigris and Euphrates in Iraq, and the Karoun River in Iran’s southwest province of Khuzestan, particularly where all three rivers meet in the Shatt al-Arab or Arvand-Rud which flows into the Persian Gulf.

Ethnicity and faith are closely connected in Mandaean identity, so there is no proselytising. Marriage with outsiders is strictly forbidden, and counts as apostasy, so anyone doing so is cast out of the faith.

As a result of this practice, the Mandaean population is constantly shrinking. But in recent years emigration has been a major factor in reducing numbers in Iran as well as Iraq.

The community in Iraq has shrunk from an estimated 70,000 to just 7,000 as members have left for Syria, Sweden, the United States, Australia and Canada as a result of the instability that followed the 2003 invasion by the US-led coalition.

In Iran, which always had a smaller Mandaean population, numbers have also fallen due to emigration. Current numbers are estimated to be between 5,000 and 10,000. After the US State Department granted Iranian Mandaeans protective refugee status in 2002, more than 1,000 moved to America.

Because the Mandaeans do not seek to convert others, they are not perceived as a threat by the Shia clerical establishment. Yet unlike other faith communities – Armenian and Assyrian Christians, Zoroastrians and Jews – the Mandaeans are not recognised as a discrete group in the Islamic Republic’s constitution, and are not accorded representation in parliament as others are.

As a result, says Farid, a Mandaean from the town of Ahvaz in Khuzestan province who emigrated to France last year, “Our children are forced to attend Koranic classes and Islamic studies because Mandaeans are not mentioned in the Iranian Constitution…. Iranian Jews, for example, can opt out of religious classes for Muslims in school.”

Farid also noted that the lack of formal recognition means that whereas other minorities may legally name children according to their religious preference, Mandaeans are required to adopt approved Muslim or Iranian names.

Shortly after the 1979 revolution, senior Mandaean clerics went to see Ayatollah Mahmoud Taleghani – an ally of Ayatollah Ruhollah Khomeini regarded as tolerant of other faiths – to ask him what freedoms they could expect under the new regime.

They were shocked at Taleghani’s response – that the Mandaeans would be “given an opportunity to convert to Islam.”

Amnesty International has highlighted violations of the rights of religious and ethnic minorities not recognised by the Iranian state, including the Mandaeans, for example when applicants are vetted for employment and higher education.

As well as discrimination, the Mandaeans also miss out by being ignored.

Their location in Khuzestan means they rarely encounter government officials from distant Tehran.

Farid says the Iranian media simply ignore the Mandaeans.

“Iranian state-run TV is constantly airing programme about religions and the beliefs of other nations, but never has a report on the Mandaeans,” he said.

Farid believes that according the Mandaeans greater recognition would benefit Iran as a whole.

“To protect the Mandaeans’ identity is to protect a part of Iran’s history that shows the antiquity of both civilizations,” he said.

In southwestern towns like Khorramshahr, Ahvaz and Abadan, Mandaean identity is as strong as ever, bolstered by time-honoured rituals centring on flowing water.

Members of the faith stand out as they immerse themselves in the waters of the Karoun dressed in their white tunics, turbans, and shawls for the Sunday ritual known as “Reshame”. Chanting prayers, a priest reminds people that the ceremony marks their covenant with God.

The Mandaean alphabet and language are derived from eastern Aramaic, an ancient tongue with common roots with Arabic and Hebrew. Although it is still the language of prayer, few young people can speak it or read the distinctive script, and most use Arabic instead.

“The Arabs of Khuzestan have good relations with the Mandaeans,” said Karim Abdian, an Arab Muslim originally from Abadan and now living in Washington. “However, Persian-speakers in Khuzestan are still unfamiliar with the Mandaeans and regard them as an Arab tribe.”

The Mandaeans of Khuzestan commonly work as merchants or goldsmiths – the latter a profession awarded them by successive Muslim rulers over time, as it was prohibited by Islamic oral tradition.

But many now live far away. The growing community of Iranian Mandaeans in the greater Washington area, for exampled, established an association in 2006 and has been encouraging new immigrants to settle there. For them, it is the rivers of another continent thousands of kilometres from the waters of the Karoun that embraces them every Sunday before flowing away like a historical memory.