The action on “Billions” takes place on Wall Street, but the masterminds of the Showtime drama are more comfortable working out of digs in the West Village. Brian Koppelman and David Levien, co-creators and showrunners, haven’t been in the space for long, but there are a few cherished mementos representing their partnership.

Koppelman and Levien met as teenagers — Brian was 16, David was 14½ — when they were sent on a summer bus tour of the American West. “That was the summer the two of us became like brothers,” Koppelman says. In a Jackson Hole, Wyo., tourist trap, after knowing each other a week, the two donned Old West garb and props for a sepia-tone photo that has survived the years. Levien points out that Koppelman is pointing a gun at him. “I don’t think the two guys in that picture ever imagined that hanging out would become our job,” Koppelman says.

The 1998 Matt Damon drama “Rounders,” about a poker ace, put Koppelman and Levien on the map. The framed call sheet for the first day of shooting was a gift from a Miramax executive. Director John Dahl was gracious and offered to let the tyro screenwriters observe the entire 44-day shoot as a crash film school course. “It was pre-dawn, in the winter, outside on Manhattan bridge and it was freezing. And it was exciting,” Levien recalls. Koppelman says the call sheet reminds them how far they’ve come. “We wrote this script in a basement with no contacts, no career and no clear prospects. It’s a great reminder of what we can do when we put our heads together.”

Wherever Koppelman and Levien find themselves working, there’s sure to be a football or two lying around. The pair regularly toss a ball back and forth inside their office when they need a break or need to work out a story problem. By now the “Billions” production crew knows to keep a few handy for elaborate location shoots. “We’ll talk about the scene as we’re throwing the football in between set-ups,” Levien says.