When I started covering the NFL in 2011, the last version of the Seahawks-49ers rivalry was still in its infancy. The Niners went to the NFC championship game that season, but lost to the Giants in a wild contest that was swung by Kyle Williams’s botched punt return. Seattle hadn’t quite reached the same heights, finishing just 7-9 that year, but the bones of the dominant Legion of Boom teams were already in place. Marshawn Lynch had rushed for more than 1,200 yards in his first full season with the franchise, and young building blocks like Earl Thomas, Kam Chancellor, Richard Sherman, Doug Baldwin, and K.J. Wright were starting to make an impact. The embers of a rivalry may have been there, but things really ignited in 2012.

That’s the year Seattle drafted Russell Wilson and the Niners transitioned from Alex Smith to Colin Kaepernick at quarterback. Over the next two seasons, those teams would lock horns in some of the most memorable and heated NFL games of this decade. And as they emerged as the best teams in football, Seattle and San Francisco redefined nearly every aspect of the modern NFL: from roster-building, to schematic approach, to how teams used their QBs.

As the Steelers-Ravens rivalry hit a relative low point in the early 2010s, with Pittsburgh slowly transitioning to the early years of its high-scoring Three-Bs era, the Seahawks and Niners filled the void. Their feud burned fast and bright, flaming out after an 8-8 finish in 2014 led the Niners to fire Jim Harbaugh. But after lying dormant for several years, it seems like both teams are finally ready to rekindle the flame. On Monday night, the 8-0 49ers host the 7-2 Seahawks in one of the biggest games of the season. The stakes between these teams are sky-high once again—and the NFL is better off for it.

It’s hard to believe that the most recent version of this rivalry lasted only a couple of years, because it gave us a decade’s worth of memorable moments. Plenty of those came when both teams shared the field, but each built their own mystique against other opponents, too. I was at Candlestick Park in January 2013 when Kaepernick racked up nearly 450 total yards and four touchdowns in a divisional-round win over the Packers. It was the most physically dominant performance I’d ever seen from a quarterback to that point—the Packers defense didn’t look like it belonged on the same field as Kaepernick.

With Kaepernick at the helm, the Niners built a reputation as a dynamic power-running squad with a hulking offensive line that could grind defenses into oblivion. And with Patrick Willis, Justin Smith, and NaVorro Bowman on the other side of the ball, San Francisco had a terrifying defense to match. Harbaugh was there to provide the comic relief with some of the most memorable sideline temper tantrums ever, and together they produced some incredibly thrilling performances. (We don’t talk about the 2012 divisional-round win over the Saints nearly enough.)

At the same time, the Seahawks emerged as the loudest (in more ways than one), coolest group in football. It had been years since an NFL team had cultivated as many personalities as the Seahawks did at the start of this decade. Sherman had no qualms about chirping in Tom Brady’s face after a win. Chancellor made a habit of erasing anyone who crossed his path. Lynch trucked countless helpless defenders on his way to becoming an icon.

The rivalry came to a head when these two teams squared off in the NFC championship game following the 2013 season. We all remember how that game ended, but before the tipped interception and the best postgame interview of all time, we got one of the greatest games in NFL history. Earlier this year, my colleague Kevin Clark and I revisited the game on The Ringer NFL Show as part of our sports Rewatchables series, and it’s incredible just how many classic moments unfolded during those 60 minutes: Kaepernick’s shredding the league’s best defense with a 58-yard scramble in the second quarter; Jermaine Kearse’s absurd catch in the fourth quarter to give the Seahawks the lead; Chancellor’s nearly exploding Vernon Davis; Wilson’s running around for eight seconds before chucking a deep throw to Doug Baldwin in one of the first huge moments of the latter’s career.

The aspect of that game that stuck out most, though, more than any individual play, was the sense that you were watching two teams that were playing a different sport than the rest of the NFL. The pure physicality and speed on display was unlike anything else in the league during that time. And in ways both big and small, the Seahawks and Niners became the teams of the era.

Beyond boasting some of the league’s biggest stars and personalities (which included their head coaches), both franchises became models for roster-building excellence. Niners fans may not have fond memories of Trent Baalke’s final days as the team’s general manager, but his early-2010s squads were absolutely loaded. San Francisco had six Pro Bowlers and four first-team All Pros on its defense in 2012 alone. The Seahawks, meanwhile, hit on a ton of late-round picks like Sherman, Chancellor, and, most importantly, Wilson. And they were the first team under the new CBA to truly understand the value of a QB on a paltry rookie deal.

The ways that both teams used their QBs also inform how teams view the position today. After decades of mostly homogeneous offensive football across the league, both the Seahawks and Niners looked at their mobile quarterbacks as opportunities, not hindrances. It’s no accident that Greg Roman, the same offensive coordinator who constructed an explosive offense around Kaepernick nearly a decade ago, is the person who’s helped turn Lamar Jackson into a superstar in Baltimore. Most of the lessons that the Seahawks and Niners taught us about the NFL are still just as applicable today.

Sadly, the rivalry vanished almost as quickly as it had arrived. Following a 2014 season that led to Harbaugh’s ousting and featured a heartbreaking Super Bowl loss that would come to haunt the Seahawks’ franchise, Seattle fell from the league’s truly elite tier—and San Francisco dropped even further than that. The Jim Tomsula and Chip Kelly eras were cringe-inducing times for the 49ersr faithful, but those tough years have made this season that much sweeter.

John Lynch and Kyle Shanahan have turned San Francisco into arguably the best team in the NFL. In a way, this year’s version of the Niners resembles the groups that were annual contenders under Harbaugh. Coordinator Robert Saleh’s defense has swarmed opposing offenses with a stacked front seven and the NFL’s most frightening pass rush. Shanahan has designed a run-heavy offense replete with ingenious ground-game designs and ideal play-action complements. Saleh has even taken up the mantle as the league’s most animated sideline presence, which I can only assume is a tribute to Harbaugh.

But while the 2019 49ers bear some resemblance to the group that kicked off this rivalry, the Seahawks couldn’t be more different. Even with famous names like Pete Carroll, Wilson, and linebacker Bobby Wagner still in place, this Seattle team wins in a much different day than it did in the Legion of Boom days. Wilson has gone from well-placed cog in an otherwise perfect machine to the most valuable player in all of football. And in possibly the most fun twist of all, Sherman is now leading the Niners defense as it torments the NFC.

Some of the particulars may be different this time around, but on Monday night, the Niners and Seahawks will once again be playing a game with crucial playoff implications. The enmity between these fan bases rivals any other bad blood in the NFL. Football is just more fun when the Niners faithful is belittling Russell Wilson, or when Seahawks fans get to remind folks in San Francisco about the 2013 NFC title. One of the league’s best rivalries is officially back, and somehow, that just feels right.