The Green Bay Packers are credited not only with being the first team to record a world championship in the Super Bowl era, but also with being the first team to repeat the achievement. More than 50 years later, the Eagles will be attempting to replicate that feat, one that has grown increasingly rare over the decades. To beat all the other teams in the NFL, the Eagles will also have to beat some heavy odds.

When the Packers' repeat closed out the 1967 season with a win over the Oakland Raiders, that wasn't even considered their most memorable accomplishment. The merger between the NFL and the AFL was three years away and the younger league was still considered far inferior. Much more attention was paid to the NFL championship game played two weeks earlier when the Packers and Cowboys somehow survived the infamous New Year's Eve "Ice Bowl," and Green Bay exited the literally frozen tundra of Lambeau Field with its fifth league championship in seven years.

After that, easing past the Raiders in the AFL-NFL World Championship Game, as it was known in the first two iterations, was an anti-climax. Things changed rapidly, of course, including the name of the game, which became officially branded as the "Super Bowl" the following year. The relative standing of the leagues was certainly never the same, either, as the Jets beat the Colts in Super Bowl III and the Chiefs beat the Vikings in the final season before the two leagues combined. Baltimore and Minnesota had the cold comfort of being the last two pre-merger NFL champions.

In any case, the Packers were the first repeaters in the Super Bowl era, even though nobody thought much of it at the time. It's a bigger deal now, and the task facing the Eagles is infinitely tougher. In a half-century since the Packers did it, only seven teams have won back-to-back Super Bowls, and it has happened only twice in the last 25 years.

To help decide if the Eagles can become the ninth team to repeat, maybe there are some clues to be found from the previous teams, some sort of a pathway to follow. Let's take a look:

Miami Dolphins, 1972-1973

All the Dolphins did was follow up the only undefeated season and postseason in NFL history with a 15-2 overall record the next season. Put it together and it was a 32-2 run. From that perspective, the Eagles, 16-3 including the playoffs last season, are already behind. While you think of the team's prolific offense from that era, led by quarterback Bob Griese, it was actually the defense that made the team special, allowing the fewest points in the league each of those years. In the 28 regular-season games, Miami's defense allowed an average of 10.7 points. It was a true sum-of-its-parts defense, with only one Hall of Fame player, Nick Buoniconti, emerging from that era.

Pittsburgh Steelers, 1974-1975 and 1978-1979

The idea of winning four Super Bowls in the span of six seasons is laughable now, but the Steelers did it easily enough. The most amazing stat from this streak is that 22 players were on all four championship teams, meaning the Steelers enjoyed unimaginable continuity under coach Chuck Noll. How much continuity? Of the 22 starters in the first Super Bowl win, 11 were still starters for the fourth. And it didn't hurt that six of them were good enough to eventually be elected to the Hall of Fame. (Not including L.C. Greenwood, somehow.)

San Francisco 49ers, 1988-1989

In 1988, the Niners were 6-5 in November and looking ordinary when Joe Montana began what was probably the hottest streak of his career, one that would see San Francisco win 27 of its next 30 games and two Super Bowls. It's easy to ascribe the success solely to Montana (and Jerry Rice), but Montana also missed significant time with nagging injuries and backup Steve Young played in a total of 21 games and started six of them. His record was 5-1. He was undefeated in his three 1989 starts and threw for more than 1,000 yards that season.

Cowboys receivers Alvin Harper left) and Michael Irvin celebrate their victory over the Bills in Super Bowl XXVII.
Doug Mills / AP
Cowboys receivers Alvin Harper left) and Michael Irvin celebrate their victory over the Bills in Super Bowl XXVII.

Dallas Cowboys, 1992-1993

The Cowboys looked like a bad bet to repeat when they opened the 1993 season with two losses, a Monday night road butt-kicking administered by the Redskins and then a flat, 13-10 home loss to Buffalo, a team Dallas had beaten by 35 points in the Super Bowl eight months earlier. Coach Jimmy Johnson didn't panic and he didn't change a thing. Of course, with Troy Aikman, Michael Irvin and Emmitt Smith, why would he? The Cowboys went 15-2 after that rough start, on the way to beating Buffalo in the Super Bowl again. (It would be the fourth straight Super Bowl loss for the Bills, all at the hands of NFC East teams.)

Denver Broncos, 1997-1998

Beginning in 1993, the NFL went to a hard salary cap that made it difficult for successful teams to keep their stars together, particularly after a championship. The Broncos' offensive core of John Elway throwing to Shannon Sharpe and Rod Smith and the running of Terrell Davis was the key to this repeat, but it was also a mentally tough team that didn't have to win pretty. In the playoffs after the 1997 season, after a win in the wild-card round, Denver went on the road to beat Kansas City and Pittsburgh by a total of seven points. The Chiefs and Steelers had been a combined 16-1 at home that season. In the Super Bowl, Elway led a last-minute touchdown drive to break a tie and beat Green Bay by seven points. By comparison, the Broncos laughed through the 1998 season and postseason to get the repeat.

New England Patriots, 2003-2004

Well, we remember how this one ended, with the Pats winning the Super Bowl by three points for a second straight year and with the Eagles executing the slowest two-minute drill in NFL history. These were really good New England teams, but – and don't take this the wrong way – sometimes it helps to pick the right opponent. The Carolina Panthers, who were 11-5 in 2003, would fall to 7-9 the following season. The Eagles, 13-3 in 2004, would be 6-10 the next year. They weren't bad teams, just fragile, and Super Bowl appearances are heavy burdens.

And that's it. Seattle had a chance to repeat in the 2014 season, but didn't; and, of course, New England ran into the wrong team last February. So, a repeat has happened just twice since the institution of the hard salary cap and not at all in the last 13 seasons.

What did we learn that gives hope the Eagles will not only get back to the Super Bowl, but win it again? We learned that offense might get the attention, but defense often provides the backbone. That continuity matters, if you can maintain it. That having a great quarterback is vital, but having a solid backup can make the difference. That staying steady through adversity is required. That sometimes being tough is more important than being pretty. And that, in how you play and whom you play, there is always an element of luck.

Put it together and that's not a bad description of the Eagles. They return a strong defense, have most of their starters back or coming back, have both a great quarterback and an MVP backup, are tough during adversity, and we'll have to see about the luck part.

Can the Eagles repeat in the Super Bowl with just what they have? Well, they are halfway there.