Footballing trends rise and fall naturally, and over the last few years we've seen several archaic methods reappear to become the norm.
We switch from zonal to man-marking at will, the striking duo is dead while the three-man defensive line is on the rise. Pep Guardiola brought Arrigo Sacchi's methods back in vogue, while he also revisited Luciano Spalletti's experiments with the false-nine.
So what's next?
It's something many try to predict, and evidence from the last several years suggests we may be moving toward a return to the libero.
The surging centre-back trend is reaching new heights with many top teams electing to break defensive strangleholds by creating mismatches with an additional midfielder.
Again, Guardiola was at the forefront of this, and during Barcelona's 3-0 victory over Athletic Bilbao in the 2012 Copa del Rey, he out-thought his mentor Marcelo Bielsa by using Gerard Pique as a deep-lying threat.
"El Loco" had accounted for all of Barca's players in a man-marking system as usual, but with Pique breaking forward, the Basque outfit had no one free to cover him. The former Manchester United man was instrumental in a one-sided result.
Now we see a stream of centre-backs who are comfortable going forward, with the likes of Toby Alderweireld, Mats Hummels, Leonardo Bonucci and David Luiz increasingly happy to move vertically in possession.
They've got the ball skills, the composure and the passing ability to be a threat.
No one has epitomized this trend as well as Jan Vertonghen in the last several months, and deputizing at left-back for Andre Villas-Boas seems to have unlocked his inner demon.
He was a "surger" at Ajax, no question; but in London, he's been fully rampant.
Take Vertonghen's WhoScored? statistics into account: three interceptions per game, 17 total key passes and a high pass-completion percentage.
Stepping out and acting is a key part of his game, and he's not alone either. Centre-backs such as Geromel and Chico are putting in more than three interceptions per game themselves.
Bielsa's use of Javi Martinez at central defence last season was tactically exciting, as the Spaniard's knack for reading the game allowed him to step out of the line and mop things up with ease.
He totaled an incredible 5.2 interceptions per game, convincing Bayern Munich to pay the €40 million necessary to land his signature.
But why does this signal a return of the libero?
It doesn't in full, but what adds to the momentum is the revival of the three-man defensive system, primarily seen in Italy's Serie A.
The libero's natural position was always that of a sweeper—the man behind a two-man defence—and from there he would break forward and attack, while on the reverse he would mop up at the back.
Take Juventus' 3-5-2 as an example. They are very much a back-three, but as Leonardo Bonucci grows in confidence and ability every single day, he's pushing forward more and making more accurate, attacking passes.
With the penchant top managers have for box-to-box dynamos such as Moussa Sissoko, Yaya Toure and Jack Wilshere, what's to stop one moving a high-energy player with defensive nous back into this position?
With many teams packing the midfield in a 4-2-3-1 formation, a libero might be a wonderful method to break down the system and overload a certain area.
The libero isn't back, but world football is moving in a direction where it could once again find a home.