Directed and photographed by Merian C. Cooper and Ernest B. Schoedsack - who would later go on to produce "King Kong" (1933) - with the assistance of journalist Marguerite Harrison, "Grass: A Nation's Battle For Life" joins a tribe of nomads known as the Bakhtiari on their gruelling annual 48 day trek across inhospitable terrain to their flock's summer pastures.

Opening with a series of frivolous scenes in which Harrison meets the tribes people, "Grass" quickly gives way to seriousness as the harsh trek takes its toll on both the Bakhtiari and the American filmmakers.

Venturing through deserts, mountains, rivers and snowy wastelands in search of the life-sustaining grasslands, the Bakhtiari's 50,000 strong caravan - complete with 500,000 cattle and goats - becomes the sole focus of the camera's gaze.

Deliberately styled as a story of man's triumph over nature, "Grass" is as much a mythic narrative of migration and settlement as a simple travelogue.

Drawing clear comparisons with the American frontier and the spirit of the pioneers (the rather glib title cards regularly mention "the Covered Wagons" of the American West), this is less an anthropological documentary than a vision of life in the wilderness filtered through the lens of American history.

So it's hardly surprising then that the film's most memorable - and protracted - sequence involves a frontier-style cattle drive across a churning river where the nomads use rafts made out of inflated goat skins (!) to get their families and their livestock to the other side.

It's a bravura sequence, and certainly one that audiences back home in the US of A would instantly relate to.

No wonder, then, that one cantankerous American preacher (quite ludicrously) claimed that "Grass" was a fake and had been filmed in the mountains around Los Angeles!

"Grass: A Nation's Battle For Life" opens at the NFT on Friday 7th March 2003.