Though the grails provide for all needs and the climate is hospitable, any further attempts to affect the environment are frustrated by the near-complete lack of metals and ores on the planet. The only building materials available are bamboo, wood, and human or fish bones and hides. Pockets of flint (eventually to be depleted) provide material for tools. With technology limited to the
paleolithic level, the bordering mountains are completely impassable, thus the only possible directions of exploration are either upriver or downriver.
However, even this travel is hindered as the Riverworld soon finds itself divided into thousands of tiny nations; empires, monarchies, republics and every other social system ever invented, each only a few kilometers long (though still with high populations; the Riverworld averages 90 people per square kilometer). Because the distribution of populations along the river seems to have been random, the character of these nations can vary wildly within a very short span. Thus, one can enter dangerously unknown and potentially hostile territory in less than a day's journey.
The reason behind the existence of Riverworld is initially a complete mystery. In Farmer's books a number of historical figures - including
Sir Richard Burton,
Alice Hargreaves,
Samuel Clemens,
King John of England,
Tom Mix,
Mozart,
Jack London and
Hermann Göring - interact with fictional characters in a quest to discover the purpose behind the creation of Riverworld and their reincarnation. Another character,
Peter Jairus Frigate, bears a striking resemblance to Farmer himself, and shares his initials. There are two versions of the character - one who appears early in the sequence, and another, being the "real" version, who concludes that the first was his brother who died as a baby, resurrected and used as a spy by the creators of the Riverworld.
During the course of the story it is revealed that the Riverworld had been created as a form of moral test for humanity. In the Riverworld universe sapience is not a naturally occurring phenomenon but is the result of a type of artificially created soul, known as a wathan. Wathans are created by a generator, a technology developed and seeded among various worlds by an unknown ancient alien race. Wathan generators create wathans which attach themselves to sufficiently advanced
chordates. Wathans are indestructible but become detached from the body upon physical death and wander the universe aimlessly and apparently mindlessly.
The first race to create wathans were only extraordinarily
adept tool users up to that point, but lacked individual
sapience. Once the first wathans were created, however, their civilization was transformed.
Self-awareness increased their capabilities by an order of magnitude, and as the creators of wathan technology, they understood it to the degree that they were able to "catch" wathans released by their own deaths, resurrecting themselves endlessly - or so they thought. They began to have difficulties in reattaching certain wathans to physical bodies, eventually finding it impossible. As this occurred only to the wisest and most ethically advanced wathans, they came to the conclusion that they were "passing on", a process comparable to the Indian religious concept of
Moksha.
With this in mind, they began wandering the universe, placing wathan generators on worlds with life that could host wathans, thereby creating other sentient species. Once they create a species they determined they could trust, they tasked them with creating yet more sapient species after the whole of their own species had "passed on". This cycle occurred several times until relatively recent times, and the creation of humanity.
Humanity's creators are a race of aliens known, among their human allies at least, as "the Ethicals." The only alien Ethical who is seen in the stories is Monat Graatut, who poses as an ally and friend of Richard Francis Burton. Monat is a tall long limbed
humanoid alien who would be instantly recognizable as non-human. The Ethicals were the ones who originally brought Wathan technology to Earth, installing both a generator and a collector. The collector would catch and store Wathans--and the human personas and memories accumulated by them--for later retrieval.
The reason for this change of policy was that humans were, to them, extraordinary. That is, humans could be both extraordinarily civilized (capable of "passing on" within a single lifetime, such as the
Buddha), and extraordinarily barbaric (capable of brutality unimaginable to any of their species, such as Nazis, the Spanish Inquisition, etc). The best of humanity was more than worthy of carrying on the cycle of creation, yet the worst of humanity obviously couldn't be trusted with wathan technology. To solve the conundrum, the Ethicals decided to put humanity to a test - the Riverworld.
Deeming that children who died before age five had not had a sufficient "chance" at life on earth they resurrected these children early on a planet known as "Gardenworld". Gardenworld was a physical paradise where the children would be raised as Ethicals by the aliens. Eventually the human and alien Ethicals began work on
terraforming the Riverworld. The idea was that every human being who ever lived on Earth would be resurrected on this planet and given another chance to embrace their better natures, thus proving themselves worthy of continuing the cycle of creation.
The entire construction of the Riverworld ecology was meant to help further this process of moral contemplation. The repetitive nature of the physical environment was supposed to encourage a concern with inward rather than outward issues. The poverty of natural resources was meant to prevent the development of a higher technology and the same old kinds of human society, and the food provided by the grails, the presence of abundant water and potential shelter, and the resurrections were meant to obviate the need for an economy or the need to strive for survival. Alcohol, marijuana, and the LSD-like dreamgum were provided for recreational purposes and as emotional enhancements to help the process to contemplation along--although the use of the drugs does not always take humans in that direction.
Origin
The original Riverworld story was titled Owe for the Flesh and ended with the protagonist (called Richard Black in this version) finding the tower at the end of the river. Farmer entered a scifi contest run by Shasta Press and subsidized by
Pocket Books, submitting his 150,000-word entry. He won the contest, but received no money. The work was never published and was lost in its original form. A later, revised manuscript (itself lost for decades) was discovered and published in 1983 as
River of Eternity.