“Don’t never look away” is the advice Irish-American gang leader Priest Vallon (Liam Neeson) gives his son just before he dies. The scene is one of the most remarkable moments in Martin Scorsese’s latest picture, Gangs of New York. And Vallon’s words could equally apply to viewers as they sit through the 168 minutes of this film.

Set during the Civil War, Gangs is the earliest chapter in what might be the most engrossing unofficial history of New York—the films of Scorsese. More than a century before Travis Bickle drove the Big Apple’s streets in Taxi Driver, the city was controlled by gangs of thugs centred around the Five Points, an intersection at the heart of the city’s foulest slum.

Herbert Asbury described these anti-heroes and their bloodiest battles in his 1928 book Gangs of New York, and Scorsese’s movie grafts a plot onto Asbury’s rambling chronicle—the story of Priest Vallon’s son, Amsterdam (Leonardo DiCaprio).

The movie’s opening sequence shows the fall of Priest Vallon and the defeat of his gang of Irish immigrants, the Dead Rabbits, at the hands of the Natives, led by Bill the Butcher (Daniel Day-Lewis). Sixteen years later, Amsterdam is released from the orphanage where he lived after his father’s death. With the help of his childhood friend Johnny (Henry Thomas), Amsterdam tries to avenge his father’s murder by killing Bill the Butcher. But when the Butcher takes a liking to Amsterdam, DiCaprio’s character becomes torn between avenging his da’ and moving up in the mob.

A distraction from the life of crime is provided by Jenny (Cameron Diaz), a petty thief who falls for Amsterdam. And as the plot, with mostly its predictable elements, moves on, the city becomes consumed by the looming draft to provide the Union army with more manpower in its war against the Confederates.

Day-Lewis’ performance as Bill the Butcher is captivating. Fitted out with bushy eyebrows and a magnificent handlebar moustache, Day-Lewis stomps around New York in a stovepipe hat and plaid pants, grinning, threatening, charming and beating his way to a crime empire protected from the police by bribery and an alliance with unscrupulous politician William Tweed (Jim Broadbent).

DiCaprio turns in a tolerable performance. He spends much of the movie squinting, fighting or crying, but he manages to portray Amsterdam without letting his pretty-boy looks turn the movie from an epic into a tearjerker. Diaz is good, with a passable Irish accent, and Scorsese’s supporting cast, including Irish gangsters John C. Reilly and Brendan Gleeson, is also memorable.

But the real reason to see Gangs is Scorsese’s recreation of mid-nineteenth-century New York. Built on Rome’s sprawling Cinecitta studio, the set is convincing down to the last blood-stained cobblestone. As the arena for bloody street brawls, the set teems with thousands of extras wreathed in smoke and drenched in blood. The fight scenes are extraordinary, gory and riveting in their savagery.

The film’s length might be inadequate; the plot seems to be shoehorned uncomfortably into the almost three hours allotted. And at its heart, the story is rather predictable and trite. But most viewers will still have a hard time looking away.