Numerous times in Napoleon, the mist settles over wintry landscapes, delicately summoning visual echoes of The Duellists, the 1977 debut feature set during the same period that put Ridley Scott on the map. Then there are muscular, large-scale scenes of warfare more characteristic of the veteran director’s later work, notably the Battle of Austerlitz, where cannon fire from Bonaparte’s army sends Austrian and Russian troops plunging to icy deaths in a frozen lake, its water stained with blood. But for all its brawn and atmosphere and robustly choreographed combat, this is a distended historical tapestry too sprawling to remain compelling, particularly when its focus veers away from the central couple.

Joaquin Phoenix’s performance in the title role is as eccentric as any the mercurial actor has given, even if his tics don’t always seem entirely grounded in character. But it’s when he’s onscreen with Vanessa Kirby as Josephine, the fallen aristocrat re-elevated by her marriage to Napoleon and then nudged aside when she fails to produce an heir, that the nearly three-hour historical epic is most alive.

The film proceeds through a timeline that will be familiar to history students, if probably not altogether lucid to anyone hoping to get a crash course here – the downfall of Robespierre; the end of the Reign of Terror; the conquest of Egypt; the 1799 coup that overthrew the existing French system of government; Napoleon crowning himself Emperor of France in 1804; the decisive Battle of Austerlitz; the failed attempts to establish peace with England and forge alliances with Prussia and Austria; the French invasion of Russia with its heavy losses; Napoleon’s abdication and initial banishment to the Mediterranean island of Elba; his return to lead France in a humiliating defeat against England; and his ultimate exile to the British-controlled island of St. Helena in the South Atlantic.

That’s a lot for any audience to digest in a single sitting, and while Scott can be commended for his ambition, neither he nor Scarpa manage to build those many plot pieces into a fluid narrative.

The through line is Napoleon’s relationship with Josephine, whom he meets at a Survivors Ball in the newly liberated Paris and marries two years later. For all his self-assurance in military maneuvers, Napoleon recognises from the outset that Josephine is his equal, or perhaps even his superior. And when he returns from Egypt indignant about being mocked in the press for her philandering, Josephine rebuffs his attempts to shame her.

That unusual dynamic between one of the most powerful men in the world and a spouse who not so long ago was in prison might have been enough to give Napoleon a more consistent pulse had their scenes together been given space to breathe and develop. But Scott is always too eager to get back out in the field, where Napoleon’s letters home to Josephine have to maintain the thread.

The film’s biggest extended set-piece is the Battle of Waterloo, with the English led by Rupert Everett drolly chewing the scenery like a scowling pantomime ponce as the Duke of Wellington. The fighting itself is expertly orchestrated, with Napoleon failing to anticipate the crushing effectiveness of frontal assault by the Brits and a flank attack by the Prussians. But the movie’s battles are more impressive in scale than in visceral impact, even with inventive use of period music and a wide-ranging score by Martin Phipps.