Ed Harris got the idea to make Appaloosa while -- where else? -- in a saddle.

The 57-year-old actor-director was on a horseback riding trip in 2005 when he read Robert B. Parker's western novel about two taciturn lawman-for-hire, Virgil Cole and Everett Hitch, tasked with cleaning up an isolated frontier town.

"I really like westerns. You get to ride and shoot," says Harris, whose career has spanned from A Beautiful Mind and Apollo 13 to The Abyss and The Rock.

"But the main thing that moved me to make the film was this relationship between these guys.

"It just happened to also be a western."

Opening today, Appaloosa marks Harris' directorial follow-up to 2000's Pollock, which won Marcia Gay Harden a best supporting actress Oscar.

"What I love about (directing) is the constant problem solving, moment by moment; it's constant decision making. I'm not that decisive a guy in my life. It's really fun to -- you don't have a choice, you have to be decisive."

And determined.

Getting any western -- hardly a genre that has set the box office on fire in recent years -- financed is a struggle.

"We fought for every dollar. (I would tell them) 'You can't do a stage coach instead of a train. If you want it to be more than an art-house western, if you want it to have production value that it deserves and calls for, you've got to give me an extra whatever it is.'

"It was pulling teeth half the time. But to their credit, they came up with the resources to get it made."

It helped, of course, to fill out the cast with such A-listers as Viggo Mortensen as Hitch to Harris' Cole, and Renee Zellweger as the unassuming femme fatale who insinuates herself into their lives.

"I thought Viggo would be great as this guy," Harris tells Sun Media.

"I thought if Viggo reads this book or sees it could be fun to do, then I don't have to explain it to him. If he gets it, he gets what has to take place between these two guys. It kind of echoes Butch Cassidy and the Sundance Kid or Robert Duvall and Tommy Lee Jones in Lonesome Dove."

Whatever reception Appaloosa receives commercially and critically -- reviews out of the Toronto International Film Festival were largely positive -- Harris says he will direct again, sooner rather than later.

"The next job won't be a directing job. I'll act in something if I can find something interesting to do.

"But I wouldn't mind directing again. I don't want to wait another eight years."