MIAMI — It was an impossibly small space to begin something so grand.

The office the Pittsburgh Steelers assigned Tony Dungy after making him the league's youngest defensive coordinator in September 1984 was deep in the bowels of Three Rivers Stadium. It was essentially an unmarked, oversized broom closet, so nondescript that visitors occasionally stumbled in accidentally, thinking it was a restroom.

The first clue that something more important was going on inside, that its occupant was putting down roots for what would become one of the NFL's great coaching trees, was the steady hum of a film projector that always seemed to be running.

Dungy was 28 at the time Steelers coach Chuck Noll handed him the job, younger than many of the players he coached. No black man had yet ascended that high up the organizational ladder of an NFL franchise. But Dungy harbored no illusions about how much tougher the climb would become for him, or any other African-American, who wanted to lead his own team. He guessed it would be another 10 years before that day came along.

"If it never happens for me," he told Associated Press sports writer Alan Robinson, who wandered into his office during his first day on the job, "I won't be unhappy."

Fast forward two decades.

Art Shell proved Dungy's prediction wrong by becoming the league's first black coach in 1989 and Dungy is now five years into his second stint as a head coach. Four of his disciples — Herm Edwards in Kansas City, Lovie Smith in Chicago, Rod Marinelli in Detroit and Mike Tomlin in Pittsburgh — now hold the same title.

The history of NFL coaching trees begins at the league's inception. But it wasn't until staffs expanded in the late 1940s and early 1950s and enough assistants moved on to become head coaches that tracing their lineage became a point of pride for the founder. One of the most notable, Giants coach Jim Lee Howell, had eventual Green Bay Packers legend Lombardi running his offense and equally legendary Dallas Cowboys coach Tom Landry calling his defenses in the 1950s.

Usually, the trees trace back not just to a founder, but to a scheme that revolutionized play. So San Francisco's Bill Walsh, whose apprentices include Mike Holmgren and Dennis Green, is forever linked with the West Coast offense, while Bill Parcells, whose students included Bill Belichick and Romeo Crennel, tend to feature some variation of the 3-4 defense.

In a similar vein, Dungy and his cohorts are usually linked to the cover-2 defensive scheme, a zone defense that leaves two safeties in deep coverage and places a premium on stopping long pass plays. Dungy learned it from Steelers coach Chuck Noll, who provided that first opportunity, and employed the scheme when he got his first head coaching job in Tampa Bay in 1996.

Dungy assembled a like-minded staff that included Smith, Edwards, Marinelli, Tomlin and former Alabama coach Mike Shula. But perhaps even more than the scheme, what linked the group was Dungy's directive that they teach instead of scream. That, and his insistence that by doing things the right way, that group of assistants would make it easier for those who followed to grab the opportunities that lay ahead.