“Fall line” has become a loaded term in the fashion world, thanks to the Vertical Catwalk, a bizarre confluence of couture and climbing that’s turning the runway on its head. The shows, set to techno, symphonies, and other tunes, send roped-in models sashaying straight down building facades. ¶ The brainchild of German Jochen Schweizer, 47, a former extreme athlete who made a 3,300-foot bungee jump from a helicopter in 1997, Vertical Catwalk has dropped in on 23 cities since 2002, including Chicago, for the gala reopening of Marshall Field’s. More than a dozen international events are planned for this fall, and a spring 2005 show at Macy’s in New York is under negotiation. Next thing you know, mountaineers will forgo crampons for Marc Jacobs heels.