Defining an era for any NFL position is messy. There are rarely clean lines to be drawn, and that means a host of complicating factors make labeling anyone the "best of his time" difficult.

I’ve always thought about wide receivers this way: The late 1980s and most of the 1990s belong to Jerry Rice. From there the baton is passed to a group that includes Terrell Owens and Marvin Harrison but is indisputably owned by Randy Moss. Beyond that is where shit gets knotty.

I signal a changing of the guard in 2007, the season that Moss broke football and Calvin Johnson became Megatron. And if that was the year that Moss fully harnessed his powers and the next age of receivers began, then the past 12 months have brought another inflection point. With Steve Smith announcing on Wednesday that Week 17’s game against the Bengals will probably be his last — during a year in which Larry Fitzgerald is pondering his football future and both Calvin Johnson and Andre Johnson already retired — the post-Moss group of standout receivers is coming to an end.

"What’s out there about these guys … it’s true," says Domonique Foxworth, a former cornerback for the Broncos, Falcons, and Ravens who now writes about the NFL for The Undefeated. "Calvin Johnson is unreal, athleticism-wise. Fitzgerald will catch anything that touches his hands. And Steve Smith wants to fight everybody. That’s what people feel about them, and those things are true."

These players inhabit a curious place in football history, in that their careers coincided with the league’s move toward modernity. During Andre Johnson’s rookie season in 2003, Buccaneers quarterback Brad Johnson led the league in pass attempts with 570. Last season 10 quarterbacks topped that figure. NFL offenses discovered jet propulsion just as this collection of players hit their prime, and it makes them the last group before what’s become the group — a younger core of pass-catching talents that features the likes of Julio Jones, Antonio Brown, and Odell Beckham Jr. and is on track to break every receiving record imaginable.

In that way and others, Smith, Fitzgerald, Andre Johnson, and Megatron authored a fascinating chapter in football history. (Anquan Boldin belongs in this tier as well, but there are no signs that he’s nearing retirement.) Unlike some of the other receiving greats the league has seen, their teams weren’t playoff fixtures. In fact, they collectively own very little championship hardware. But each has put together a body of work that warrants mention alongside the best ever, and as their careers wind to a close, it’s a good time to take stock of where they stand — as a group and compared to one another — in NFL lore.

Let’s get this out of the way first: One of these guys exists on a plane above the rest, and that guy is Calvin Johnson. Inevitably, any debate over the merits of comparable players is colored by the value system of who’s making the argument. To me, a player having transcendent talent during a truncated career — no matter the length — is more notable than compiling steady statistics for a decade and a half. By his second season, Johnson was living in SportsCenter highlights. As fantasy football took over the world, Megatron was one of its conquering rulers. In every way, Megatron was the wide receiver position from 2008 to 2013.

Even including the last couple of years of his nine-season tenure in Detroit, Johnson’s numbers by age 30 rival anybody. Only Moss, Fitzgerald, and Brandon Marshall had more catches among receivers than Johnson’s 731 before turning 31, and only Odell Beckham Jr. (97.1) and Julio Jones (96.8) have averaged more yards per game (86.1). Just three receivers ever — the big two, Jerry Rice and Moss, and Fitzgerald — caught more touchdown passes.

Johnson’s 2012 campaign still looks like a misprint: 122 catches for 1,964 yards. The clips of him from that year are fascinating. On nearly every play, he was bracketed by at least two defenders. It never mattered. He was an unstoppable force, undeterred by scheme or extra attention. That fall, he became appointment viewing in a way that few receivers outside the Moss-Rice echelon ever do.

Even more than the numbers, that’s the aspect of Johnson’s career that will endure. He was a modern marvel, from his days at Georgia Tech to his final game with the Lions. Foxworth was a senior at Maryland the first time that he played against Johnson. He can still recall a specific play from that game — Johnson running a deep dig across the middle of the field, Foxworth recognizing it, and Johnson almost levitating to corral an overthrown pass.

"He went up to a floor higher than I can reach," Foxworth says.

The 240-pound Johnson slammed into Foxworth’s chest as they hit the ground, and in that moment the future third-round pick was glad his college career was ending. "You feel like you’re ready to go to the NFL because you’re dominating the level you’re on," Foxworth says. "But I felt like I needed to go to the NFL because I didn’t want to go up against him any longer."

A wideout with a tight end’s build who could run the 40-yard dash in 4.35 seconds, Johnson was closer to the Loch Ness monster than he was to any of his contemporaries — the type of mythical figure better suited for shaky, grainy footage than high-definition broadcasts beamed to our living rooms. Megatrons don’t come along once in a generation. They come along once. He stands alone in this group and warrants mention for any blueprint of a wide receiver Mount Rushmore. We won’t see another Calvin Johnson.

After Megatron, though? That’s where it gets trickier. The legacies of Smith, Fitzgerald, and Andre Johnson are less defined, especially in regard to how quickly each could make the Hall of Fame.

In evaluating the other three receivers in this conversation, there’s a crucial bit of context to establish up front. As the Canton debates for Johnson (from here on out, that’s Andre; I’ll use "Megatron" when referring to Calvin to avoid confusion), Smith, and Fitzgerald begin, one of the first hurdles those players will have to clear is the group of highly productive receivers still waiting on their busts. As Rick Gosselin, the longtime Dallas Morning News columnist who’s been a Hall of Fame voter for 28 seasons, says: "Do I think these guys are better than Isaac Bruce, Torry Holt, and Reggie Wayne? Not necessarily, and those guys can’t get in."

By the numbers, the trio that Gosselin mentions lines up well with the Fitzgerald-Smith-Johnson group. Five of the six have between 70 and 91 career touchdowns (with Fitzgerald way ahead of the pack at 103), and the same number have at least 14,000 receiving yards. (Holt lags slightly behind with 13,382, but he played only 11 seasons.) An important distinction, though, and one that figures heavily into any argument for the guys who played in 2016, is the quality of quarterback play they had.

Wayne lived the most charmed life a wide receiver can ever dream up. Of the 221 games he played with the Colts, either Peyton Manning or Andrew Luck started 205 of them. The missing 16 came from the 2011 season that Manning sat out because of a neck injury. It was also the first time in eight years that Wayne slipped below the 1,000-yard-receiving plateau.

It’s easy to tie Bruce and Holt to Kurt Warner, but the Greatest Show on Turf was shorter lived than I remember; Warner started seven more games with the Cardinals (57) than he did with the Rams (50). For his part, Bruce put up monster numbers long before Warner arrived: He enjoyed the best statistical season of his career (119 catches for 1,781 yards with 13 touchdowns) in 1995 with 13 games of some guy named Chris Miller playing quarterback. Still, for almost all of Bruce’s and Holt’s careers, they enjoyed lining up alongside Warner or the more-than-dependable Marc Bulger.

Fitzgerald played with Warner from 2005 from 2009, but there were plenty of seasons in which I assume he’d have done despicable things to catch passes from Bulger. His stretch of Arizona quarterbacks between 2010 and 2012 was truly the dark ages for a wideout. If there are small children around, shield their eyes before reading this list: Derek Anderson, John Skelton, Max Hall, Kevin Kolb, Ryan Lindley, and Brian Hoyer. In 2011 — in nine games with Kolb and seven with Skelton — Fitzgerald finished with 1,411 receiving yards, fourth in the NFL. There’s no proper athletic equivalent of that; it’s like running a four-minute mile without wearing shoes on a track covered in broken glass. The Cardinals got Carson Palmer for some athletic tape and helmet screws in April 2013, and no one would have blamed Fitzgerald for hugging him as he walked in the door.

It speaks to how bad the circumstances were for Johnson and Smith that Fitzgerald might have had the best quarterback situation of the three. After four years of David Carr, Johnson’s numbers exploded when the Texans traded for Matt Schaub before the 2007 campaign. From that year until Schaub got the pick-six yips in 2012, Johnson was a force of nature anytime he was on the field (6.5 catches and 93.5 yards per game). Jake Delhomme suffered a similar implosion during the 2009 season, at the end of his seven-year run as Steve Smith’s quarterback with the Panthers. Smith has enjoyed better quarterback play during the past six seasons (first with Cam Newton in Carolina and then with Joe Flacco in Baltimore) but before 2011, former NFL Europe star Delhomme was by far the best passer he had ever played with in the pros. Delhomme enjoyed a handful of productive seasons, but Manning (or Warner) he was not.

That’s what makes the careers for all three of these receivers even more remarkable, and in my mind, superior to those of the Bruce-Holt-Wayne trio. Without anything resembling top-tier quarterback play, they’re still among the most productive wideouts in NFL history.

There are no qualifiers necessary when talking about the numbers the post-Moss group has amassed. They’re some of the most prolific pass catchers the league has ever seen. Fitzgerald has 1,120 career catches, more than any wideout except Jerry Rice. Johnson is ninth on the all-time list at 1,062, and Smith is right behind him with 1,028. In terms of yardage, Smith ranks sixth (14,697), Fitzgerald ranks eighth (14,346), and Johnson ranks 10th (14,185). Touchdowns — where Fitzgerald sits sixth at 103, considerably ahead of the others — are a different story, but we’ll get to that.

Based on those totals alone, it would seem like all three deserve mention among the best receivers of all time, but Gosselin is quick to point out that parsing their gaudy figures becomes difficult. "The problem with this committee is that we’re trying to figure out whether these statistics are a product of the ability of the player or the style of the game," Gosselin says. A litany of factors — from rule enforcement to the proliferation of the short passing game as an alternative to rushing — has made a receiver’s life easier than ever. As it’s gotten simpler to rack up completions, identifying the benchmarks that define greatness has only gotten more complicated.

"If you’re a quality receiver [now], in my eyes, you should have 100 catches in a season," Gosselin says. "You should have 1,000 catches in your career. And that’s where it gets dicey."

During the Cardinals’ Week 15 loss to the Saints, Fitzgerald became the most targeted receiver in NFL history (he’s currently at 1,874). Both Smith and Johnson also rank in the top seven. It’s those bits of context that make separating production from era-based opportunity difficult.

In Gosselin’s mind, Fitzgerald’s dominance transcends this. His line of 1,000-plus catches, 14,000-plus yards, and 100-plus touchdowns stands out regardless of era. With Smith and Johnson, some of the totals are more problematic. Johnson’s career stats suffer because of injury; despite entering the league a year before Fitzgerald did, he played in eight fewer games. And while Johnson’s per-game production rivals anyone — he averaged 80.5 yards per game during his time with the Texans, which would have been the third-best figure ever (behind Megatron and Antonio Brown) had he not spent two forgettable years bouncing around the AFC South — his touchdown total is mystifyingly low. His 70 career scores puts him one spot behind former Patriots burner Stanley Morgan, who scored 72 on 505 fewer receptions. Considering Johnson’s overall volume, that just doesn’t make sense.

One simple explanation is that Johnson lacked the opportunities afforded to many of his All-Pro peers. In the 2012 season, when he finished with 112 catches and 1,598 yards, he scored four times. Only seven of his 162 targets came in the red zone, and Texans teammates Owen Daniels and Arian Foster both saw more passes inside the 20. That’s not an anomaly. The year before, both Jacoby Jones and Kevin Walter had as many targets as Johnson inside the 10. There were seasons (2008 and 2009) in which Johnson’s red zone work paralleled his target share elsewhere, but even then, his usage near the goal line put him in the middle of the pack among receivers leaguewide.

Smith’s touchdown total (81) is less alarming, but his detractors will likely point to the longevity of his career as the primary reason he’s been able to pile up these numbers. In essentially 14 seasons (discounting his rookie season spent as a kick returner and the 2004 campaign he missed with a broken leg), Smith has topped 1,400 yards twice, the same number of times he’s been an AP first-team All-Pro.

But to take all those numbers at face value diminishes the way Smith did most of his damage. His raw numbers may be less striking, but there’s an argument to be made that he was more dangerous with the ball than either Johnson or Fitzgerald at their peaks.

To separate game-breaking touchdown potential from opportunity-based scoring, I took a deeper look at each of Fitzgerald’s, Smith’s, and Johnson’s scores. Of Fitzgerald’s 103, fewer than half came on passes of 10 yards or more. At 51, he’s only 13 ahead of Johnson by that breakdown. The biggest revelation is Smith blowing them both out of the water with 66 touchdowns of 10 yards or more. So while Johnson’s touchdown total shouldn’t be held against him the way it likely will be, Smith’s figure may be even more impressive than it looks on the surface.

Think about being in a room with four dozen other Hall of Fame voters trying to sift through the nuances of how a player caught 1,000 career passes in the NFL. With more receivers than ever hitting previously untouchable statistical benchmarks, a logjam during the voting process is all but guaranteed. "What happens is, if two or all three of those guys make the room, they tend to split the vote," says ESPN senior writer Jeff Legwold, who’s been on the selection committee since 2009. "So then they keep coming back. And then you have a backup because more players are coming into the queue."

As the stats grow tougher to translate, what it was like to watch these guys — and to coach and play against them — becomes a critical part of the equation in deciding how these receivers stack up. Legwold and Gosselin both use the word "impact." It’s a nebulous term that can apply to anything from performance in pivotal games to memorable plays to what sort of bogeyman a receiver was to defenses.

For Johnson, those elements pull in different directions. When he was drafted in 2003, the NFL hadn’t seen many receivers with his combination of size and speed. At 6-foot-3 and 230 pounds with 4.4 40 speed, Johnson was the receiver sent here from the future — Megatron before Megatron.

"A healthy Andre Johnson was hell," says former Steelers cornerback and current NFL Network analyst Ike Taylor. "He was a mutant."

Because Johnson had the speed to threaten cornerbacks over the top and the frame to shield anyone tasked with covering him, the in-breaking routes favored in the Texans’ play-action-heavy offense were there for the taking. To watch him on a deep dig or skinny post was to see an artist at work. He was a chains-moving monster, a master technician in the open field who just so happened to be built like Captain America.

Johnson’s problem is that Hall of Fame busts aren’t carved from 18-yard dig routes. His career lacks the high-profile moments that so many great receivers had. It took until Johnson’s ninth season as a pro for Houston to reach the playoffs, and when he did, backup T.J. Yates was playing quarterback. Johnson was a quiet man whose career was filled with quiet, often unseen brilliance.

Fitzgerald, on the other hand, hasn’t needed many trips to build a lasting postseason legacy. His run in the 2008 playoffs remains one of the best stretches any player — at any position — has ever had. During Arizona’s charge to Super Bowl XLIII, Fitzgerald racked up at least 100 yards and a touchdown in each of the Cardinals’ four games. No player has ever matched those totals more than twice in a single postseason. If Santonio Holmes’s ballet act in the back corner of the end zone hadn’t won the Steelers that game, Fitzgerald’s 64-yard touchdown with 2:37 remaining would’ve been the catch that echoed for the rest of time. It would have been a fitting end to a postseason that Fitzgerald had defined. During those four games, no one would have argued that he wasn’t the best the NFL had to offer.

Unlike Megatron and Johnson, there was nothing superhuman about Fitzgerald in his younger days. "He kind of had a Jerry Rice aspect to him in that you’d watch him and think, ‘Eh,’" Foxworth says. "He’s not shaking anybody. He’s not running away from anybody."

Fitzgerald’s distinguishing trait was always his hands. If the ball was thrown into his orbit, he found a way to come down with it. "His one standout thing is his ability to catch anything," Foxworth says. "And that requires DBs to play him tighter than they’d play anybody else. That has the same impact as shiftiness."

As Fitzgerald has moved into the slot late in his career, his ability as a big-bodied physical blocker took him from being a matchup problem to being a schematic one. As longtime defensive coordinator Mike Nolan points out, it’s become difficult to distinguish how many tight ends the Cardinals had on the field. "He’s such a good blocker and he’s so physical that it throws you off as a defense," Nolan says.

While Smith, at a diminutive 5-foot-9, may not be built like Fitzgerald, his tenacity as a blocker is among the first things former opponents mention when discussing his game. Foxworth says that the beginning of every matchup with Smith was a test designed to allow Smith to feel out how easily he could torment the guy across from him.

"Pretty much the beginning of any game I played against Steve Smith, he would — for lack of a better term — see if you were about this life," Foxworth says.

The difference between Smith and other marquee receivers, Foxworth says, is that there was never a break. "You had to be on your toes every single play," Foxworth says. "He’s either going to fight you or try to run past you."

Plenty of physical, punishment-inducing receivers have come through the NFL, but not many could roast a defense the way Smith could on his best days. Smith’s 2005 campaign, coming off a broken leg suffered in Week 1 of the previous season, was one for the ages. He caught 103 passes for 1,563 yards with 12 scores, including six touchdowns of at least 33 yards. After tallying 10 catches for 84 yards with a score in a win over the Giants in that season’s wild-card round, Smith took a flamethrower to a Bears defense that had allowed a league-best 12.6 points per game: 12 catches, 218 yards, and two scores in a 29–21 divisional-round victory.

Asked which of these three receivers he’d have wanted to play with the most, Taylor takes less than a second to answer. "Steve Smith," Taylor says. "He is a Pittsburgh Steeler."

Taking into account every factor influencing how this group of post-Moss receivers will be remembered, a hierarchy comes into focus. Megatron’s short but brilliant run claims the top spot, Fitzgerald and his absurd production follows, and Smith and Johnson — in that order — round out the four. Megatron and Fitzgerald are both likely headed for the Hall of Fame; the arguments for Smith and Johnson get tougher when weighing some of the circumstances that played into their penchant for piling up numbers.

One final piece that’s key to the legacies of Smith, Johnson, and Fitzgerald is their roles in elevating their respective franchises. In the days before Arian Foster and J.J. Watt, Johnson was the face of the Texans; he’s still the most accomplished player in franchise history. No one on the offensive side of the ball came close to achieving what Smith did in a Panthers uniform, and Fitzgerald is the living, breathing embodiment of the Cardinals’ emergence from the dregs of the NFL.

As a group, they helped to create an era of wide receivers, and individually each helped to define the best period in a franchise’s history. There may be holes in their Hall of Fame résumés — they played in a cushy period for pass catchers and don’t have a single Super Bowl title to go around — but there’s no denying that this was the group that lifted the position to new heights and ushered in the era of the wide receiver.