Archaeologist Francois Marneau (Max von Sydow) persuades the French military to send another division of the Legion to provide security for him on his resumption of the dig.
Commanding these soldiers is the slightly-shell-shocked Major William Sherman Foster (Gene Hackman), a tough, no-nonsense officer who makes no bones about his dislike for Marneau's ambitions, dismissing it as "grave-robbing" and pointing out that not only the treasures believed to be hidden at Erfoud rightly belong to the locals, but that the lives of his men are more valuable than anything that can be dug out of the ground.
Among Foster's force are a number of new recruits, including roguish jewel thief Marco "The Gypsy" Segrain (Terence Hill) and giant White Russian Ivan (Jack O'Halloran aka Non from Superman II).
Accompanying Marneau is the daughter of one of the kidnapped curators, Simone Picard (Catherine Deneuve), who soon falls for the charming Marco, even though she tries to keep him at arm's length because of her past experience with a solider during the war.
The site at Erfoud is the final resting place of a Berber saint, The Angel of the Desert, which Bedouin warlord El Krim (Ian Holm) is using as a catalyst to unite the various tribes of the region in a holy war against the foreign invaders.
The bulk of March Or Die focuses on the hard training regime and merciless discipline of the French Foreign Legion, and these are the most compelling parts of the story as it builds towards its blood-soaked climax that is more Alamo than Zulu.
The romantic sub-plot between Mme Picard and Marco - although it adds emotional impact to the film's coda - feels slightly superfluous to modern sensibilities. There is an attempt to create a love triangle by playing on Foster's attraction to Picard, but it doesn't really go anywhere.
Also the casting of Ian Holm as El Krim, while de rigeur when this film was shot, now undermines the charisma of the Bedouin leader, making him more akin to a character in Michael Bentine's Potty Time than a fearsome warrior.
While Marco is the nominal hero of March Or Die - looking after his friends as they struggle with the training, wooing the female lead, standing up to authority and learning to respect it etc - Gene Hackman steals the show because he's Gene Hackman.