In football, offense tends to be what dominates the headlines and sells tickets. The flash of a big play and the thrill of a long touchdown are what drive TV ratings and are the things that fans love to watch. But for all the glamor surrounding the offensive side of the ball, there’s a reason the age-old adage is “defense wins championships.”

You’d be hard-pressed to find a successful NFL team that did not have a defense that bullied its opponents off the field and dramatically impacted nearly every single game. A great defense’s ability to suffocate an offensive attack makes it a unique commodity in sports—a unit that has just one job but whose performance nearly always determines the final result of the game.

One of the ways a great defense operates is by psychologically destroying its opponent before they even set foot on to the field. Often, these units carry nicknames like the “Steel Curtain” or the “Purple People Eaters,” monikers that only add to their legend and give opposing offensive players nightmares days before the actual game. Even if they didn’t always win Super Bowls, these ferocious teams have lived up to their lofty reputations and cemented their legacy as all-time greats. These are The 10 Most Intimidating Defensive Units in NFL History.