HBO has officially greenlit Lewis and Clark, a six-hour miniseries that will chronicle the pair's exploration of the Louisiana Purchase. Starring Casey Affleck as Meriwether Lewis and Matthias Schoenaerts as William Clark, Lewis and Clark has even bigger names serving as executive producers. Tom Hanks, Brad Pitt, and Edward Norton are among seven people backing the miniseries. It's based on the book Undaunted Courage by Stephen Ambrose, who also wrote Band of Brothers — another project Hanks famously helped bring to HBO in collaboration with Steven Spielberg.

Production is scheduled to start sometime this summer, but there's no word yet on when it will begin airing on the network. Late last year, it was reported that HBO was putting out casting calls for Montana natives. Casting directors were seeking out people familiar with speaking Native languages including "Shoshone, Nez Perce, Mandan, Hidatsa, Arikara, Blackfeet, Chinook, Clatsop, Walla Walla, Sioux and Shawnee." John Curran (The Painted Veil) will be directing the miniseries and sharing writing duties with Michelle Ashford (The Pacific) and Norton. Here's HBO's synopsis of what viewers are in for: