The Mandaeans are the last surviving Gnostic community with an unbroken tradition, and their religion is bound to this river system in a way few others are bound to any geography.
Their central rite is immersion in flowing water, performed frequently rather than once, by a priest, in a river, with a specific liturgy; their word for such water is yardna, the same root as Jordan, applied to any living stream. They honour John the Baptist as a great teacher, reject Jesus as a false messiah, use a distinct script and an Aramaic dialect of their own, and possess a substantial body of scripture including the Ginza Rabba. Priesthood is hereditary and the ritual requirements are demanding, which makes the loss of priests a direct threat to the religion's continuation.
The community lived along the lower Tigris and Euphrates and in the marshes between them, in Iraq and southwestern Iran, for at least a millennium and a half. Jorunn Buckley's work with the community and its manuscripts documents both the tradition and its scribal transmission, which she has been able to trace through colophons back many generations.
Since 2003 the Iraqi Mandaean population has collapsed, from tens of thousands to a small remnant, through targeted violence and emigration. Most Mandaeans now live in Australia, Sweden, the United States and elsewhere, in places with no river a priest can use, and how the rite is to be maintained is an open and pressing question for the community.