The six-hour miniseries is based on the book "Undaunted Courage" and hails from exec producers including Tom Hanks, Brad Pitt and Ed Norton.

HBO is moving full steam ahead with its long-gestating Lewis and Clark miniseries.

The premium cable network has tapped Casey Affleck to star in the six-hour mini, The Hollywood Reporter has learned.

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Based on Stephen E. Ambrose's book Undaunted Courage, Affleck will star as Meriwether Lewis in the story of America's first contact with the land and the native tribes of the country west of the Mississippi River. The drama tells the epic journey of the Corps of Discovery and its captains, Meriwether Lewis and William Clark, as they traverse uncharted territory on a mission to deliver President Jefferson's message of sovereignty and search for the fabled all-water route to the Pacific.

The mini will focus on the achievements of Lewis and Clark as well as the physical, spiritual and emotional toll the expedition takes on them.

The drama hails from HBO and National Geographic Entertainment and is produced by Playtone, Plan B and Class 5. Playtone's Tom Hanks and Gary Goetzman, Plan B's Brad Pitt and Dede Gardner as well as Class 5's Edward Norton will executive produce. Norton, John Curran (The Painted Veil) and Michelle Ashford (Showtime's Masters of Sex) will pen the script.

For his part, Affleck will next be seen in Christopher Nolan's Interstellar opposite Jessica Chastain. His credits include Out of the Furnace and The Assassination of Jesse James by the Coward Robert Ford, for which he earned an Oscar nomination. He's repped by WME.

Email: Lesley.Goldberg@THR.com

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