Before Peyton Manning was the first pick in the 1998 NFL draft, and before he stood at the offensive line and flapped his arms, and before he ever screamed “Omaha!” the Denver Broncos strapped their hopes to Terrell Davis’ back and let him carry them to a Super Bowl.

In the season before Manning landed with the Indianapolis Colts, Davis carried the ball 369 times in the regular season and then 30 more times in a Super Bowl victory over the Green Bay Packers. Quarterback John Elway attempted only 22 passes in the Super Bowl.

Then, the NFL was still a world where being a running team was a viable option. You ran to win. Everyone wanted a Davis, a Barry Sanders or an Emmitt Smith. Sanders at one point was the highest-paid player in the league, unfathomable in today’s NFL.

But it wasn’t in 1997. Teams ran on 55.46 percent of their plays that season. The high-powered aerial offenses, which are also now more protected by the league, hadn’t been birthed yet.

Then Manning came. And his arms flapped, and he gestured and he yelled, causing — at least in part — the league to change into one that valued the pass more than the run. It was like nothing the league had ever experienced. He became a coach on the field, and the Indianapolis Colts transformed into perhaps the best passing attack the NFL has ever seen.

“Watching him on the field was almost like watching someone at the control panel of a massive operation,” said Field Yates, an ESPN analyst and former NFL scout. “He always knew what was going on in front of and around him, and the way he was able to adapt pre-snap is something, in my estimation, that has influenced the league and game of football as a whole.”

The debate over where Manning ranks among NFL greats will continue to rage over the next several years. He won only two Super Bowl rings, well behind Tom Brady (four and counting) and San Francisco 49ers legend Joe Montana (four). But Manning’s impact on the game can never be questioned.

He changed how the position is played. Instead of what happened during the play being the most important thing, Manning made what happened before each snap equally important. He turned the art of preparation into a requirement of the position.

No longer could quarterbacks simply walk to the line with an audible or two in their back pocket and go to work. He made it so that modern quarterbacks had to read and dissect the defense and put the offense in the best position to succeed.

And no, he wasn’t the first quarterback to do these things. He just did them better and at a higher level than anyone who came before. Whoever comes after him will be required to go through the often painful and tedious process to always be the smartest and most prepared player on the field.

“It was a treat for an ex-quarterback to watch Peyton Manning work and prepare and play the game,” Broncos general manager John Elway said. “I call it the ‘old days.’ We’d get the snap and try to figure out coverage on the way back, make our reads there and go from there. Peyton Manning revolutionized the game. We always used to think no-huddle was fast-paced — get to the line of scrimmage and get people off balance. Peyton revolutionized it: ‘You know what? We’re going to get to the line of scrimmage, take our time. I’m going to find out what you’re doing, and then I’m going to pick you apart.’”

And as Manning has often said, the job isn’t easy.

“If you ever feel like that’s not important — like, ‘Hey, I don’t need to watch last season; I know what we did; I know what I did wrong’ — no, you don’t know,” Manning once told ESPN. “You need to watch it. Watch the bad plays. It’s not fun to watch bad plays, to sit there and say, ‘That’s a bad decision’ and ‘Horrible read.’ No matter how old you are, you need to go into that prepared to be constructively criticized and learn how to grow out of the mistakes every year.”

Being at the forefront of enhanced quarterback play also was a major benefit for Manning’s career in other ways. And it has helped every quarterback who has come along since.

As players like Manning and Brady became so important to their teams and the marketability of the league, the rule book changed to protect them.

By the time Manning walked away this week, the league had changed to the point where it was difficult to even hit a quarterback. You can no longer hit quarterbacks high or low or after they let the ball go. Receivers can’t be checked or bumped too far down the field. Over the years, the pocket has become the safest place on a football field.

All of this has helped lead to the rise of the quarterback. It helped Manning walk out of the NFL as the leader in virtually every passing category, and it’s the reason Saints quarterback Drew Brees likely will pass some of those marks before he walks away.

There’s a reason teams rushed on only 42.5 percent of the offensive plays last season, and it wasn’t because the quarterbacks are that much better than they were back in 1997. It’s just easier to pass now.

You can argue that Dan Marino would have had more than one 5,000-yard passing season if he had entered the league in 2003 instead of 1983, or that Montana’s stats would have been gaudier. And it can be argued that if Manning had come years before, he wouldn’t have had the same numbers or longevity if defensive ends had the green light to hit him the way they once did.

But all of that is part of Manning’s impact on the sport. He helped make quarterback play the most marketable thing in the sport. And it’s unlikely the change in rules will be the thing people remember most about Manning or any other current quarterback’s legacy.

When Yates looks back at Manning’s career, he sees impact off the field. He sees smarter media and smarter fans. He sees a legacy that not only caused quarterbacks and defenses to get smarter. He feels as though Manning made even people who watched the game become more intelligent.

“I think Peyton elevated fans’ awareness of the mental aspect to football,” Yates said. “He had incredible physical gifts that were matched by an equally rare football IQ. Be it from his legendary preparation or his on-field adjustments, he made fans more acutely aware of what goes on between games and between plays.”

And that should be Manning’s legacy: He made everyone who ever played alongside him, prepared to face him or watched him play the game better at what they do.

THE QUARTERBACKS A.P. — AFTER PEYTON

After Peyton Manning’s retirement, these three are the NFL’s veteran leaders at quarterback:

Drew Brees, Saints

Becomes the active leader in passing yards (60,903), touchdowns (428, tied with Tom Brady), completions (5,365), attempts (8,085) and interceptions (205) with Manning’s retirement. He needs 11,037 more passing yards to pass Manning, which would require him to average 3,679 yards in each of the next three seasons. To catch Manning in touchdowns, he’d need to average 38 per season over the next three years.

Tom Brady, Patriots

Considering Brady will turn 39 before the start of next season, Brees should be able to outlast him in the battle for those career marks. While Brady is on Brees’ heels with 58,028 career passing yards and is tied in touchdowns, the only way he should end up topping Brees is if he manages to outlast him and continues to play at a high level. It seems unlikely, but Brady has turned beating time into a cottage industry.

Aaron Rodgers, Packers

The Green Bay star has a long way to go before he can even think about Brady and Brees, let alone the lofty marks Manning leaves behind. The 32-year-old is sitting on 32,399 passing yards and 257 touchdowns. He would need to average more than 3,900 yards in each of the next 10 seasons to catch Manning. The odds are against him, especially since his single-season high in passing yards is 4,643.