HBO‘s long-gestating six-hour miniseries Lewis And Clark has taken a big step towards fruition with the casting of Oscar-nominated Casey Affleck (The Assassination Of Jesse James By The Coward Robert Ford) as Lewis. Lewis And Clark, executive produced by Tom Hanks, Brad Pitt and Gary Goetzman, is based on the book Undaunted Courage by Stephen E. Ambrose. It tells the story of America’s first contact with the land and native tribes of the country west of the Mississippi River. It chronicles the epic journey of the Corps of Discovery and its captains Meriwether Lewis (Affleck) and William Clark traversing uncharted territory on a mission to deliver President Jefferson’s message of sovereignty as they search for his fabled all-water route to the Pacific. Lewis And Clark, from HBO and National Geographic Entertainment, is produced by Playtone, in association with Pitt’s Plan B and Class 5. Dede Gardner and Edward Norton also are executive producers. John Curran directs and co-wrote, along with Norton and Michelle Ashford. WME-repped Affleck can next be seen opposite Jessica Chastain in Christopher Nolan’s Interstellar.