When Arsenal were building the Emirates, Arsene Wenger wanted the Gunners' new stadium to be like the Mestalla.

On previous visits with Arsenal, he'd been struck by the steepness of Valencia's ground. Would it be possible, Wenger enquired, for the Emirates to mimic the claustrophobic Mestalla, complete with steep stands that felt like four vertical walls? Alas, building regulations in Britain differ from those in Spain, and Arsenal were forced to settle for a significantly lesser gradient -- 7.5 percent less steep, to be precise.

That's just one small tale that illustrates the extent of Wenger's influence upon Arsenal, and his influence upon their ground. It was peculiar to see someone else other than Sir Alex Ferguson in the home dugout at Old Trafford in 2013, but it will be even stranger to witness someone other than Wenger in the ground he helped to design.

His replacement is Unai Emery, and while the Spaniard's architectural preferences are unlikely to be relevant during his three-year contract, Emery will be hoping to conjure up the Mestalla spirit this weekend for his meeting with compatriot Pep Guardiola. It was at the Mestalla where Emery and Guardiola played out amongst the most fascinating, enthralling, high-tempo tactical battles of recent years, during their days at Valencia and Barcelona respectively.

Yes, the headline figure you'll read this weekend is 0-4-6: Emery didn't manage a single win against Guardiola. That's a disappointment rather than a scandal, for Guardiola's Barcelona were the world's greatest side, perhaps the best of modern times. Look beyond the score lines and assess the pattern of play, and you'll discover some absolutely wonderful contests that Valencia regularly dominated -- largely thanks to Emery's clever game plans.

The major theme was Emery always deployed a natural left-back on the left of midfield. Sometimes this was Jordi Alba, pushed forward into his old position on the flank, but on other occasions he was deployed at left-back with Jeremy Mathieu ahead of him. Emery deployed two left-backs in tandem because he was concerned by the threat of Barca's Dani Alves speeding forward on the overlap, the type of tactical concession Wenger would rarely make.

Notably, however, Alba and Mathieu also offered a great attacking threat, and regularly caused Barcelona serious problems going forward. Indeed, both performed so impressively against Guardiola's side, on such a consistent basis, that Barca eventually signed both. Mathieu was most regularly deployed at centre-back after his switch to the Camp Nou, summarising what a functional left-winger he'd been in those matches against his future employers.

Pep Guardiola has never lost to Unai Emery head-to-head but that doesn't mean Emery hasn't posed him problems tactically. JOSEP LAGO/AFP/Getty Images)

In those contests, Valencia were reactive but positive. Emery modified his usual system to nullify Barcelona's most dangerous weapons, but his players pressed high, enjoyed long spells of possession and maintained an aggressive defensive line. In almost every game, Valencia would dominate the opening period, force Guardiola to formulate an entirely new tactical solution, and Barca would launch a fightback. In March 2010, for example, Valencia's midfield pressing proved so effective that Guardiola switched to a 4-2-4 formation for the first time, forcing Valencia's holding midfielders higher up the pitch when pressing, and creating space between the lines for Lionel Messi, who took advantage of substitute Thierry Henry's tremendous hold-up play, in arguably the Frenchman's last top-class game. Barca struggled badly in a goalless first half, but won the second period 3-0.

Seven months later, Valencia again dominated the first half, with Alba and Mathieu doubling-up against Messi on the right. Valencia went 1-0 up, but again Guardiola changed things: Messi moved central, Andres Iniesta deeper, Barcelona played more direct, and they won 2-1. "In the first half we were passed out of the game, in the second we were much better," said Guardiola. That would be the regular pattern.

Sure enough, in March 2011, Guardiola pre-empted Valencia's strategy down the left, so he pushed Alves forward in a 3-5-1-1, a formation almost never witnessed during Guardiola's stint at the Camp Nou. Mathieu was again outstanding, Valencia again dominated, Guardiola shifted system completely to a 4-3-3 and Messi scored a late winner in a 1-0 win.

In Sept. 2011, meanwhile, Guardiola again pushed Alves on, this time going for a 3-3-1-3. Valencia, as always, dominated the first half down their left, and twice led -- the second time for 54 minutes. Guardiola was forced to re-shape and ended up with Alves at right-sided centre-back and Adriano on the right of a front three, essentially replicating Emery's double-full-back plan. It finished 2-2.

If Emery brings the same approach to Arsenal, it will represent a significant revolution -- even if "playing impressively and not winning" feels somewhat familiar. It's about how and why Emery's side played well: they acknowledged the opposition's strengths and their manager had devised an appropriate game plan. Wenger was a reluctant tactician, only bothering to speak about the opposition in pre-match briefings relatively recently.

Emery will say the right things about possession play and attacking football, and with players like Mesut Ozil, Henrikh Mkhitaryan and Pierre-Emerick Aubameyang, Arsenal will continue to entertain. But Emery is a strategist rather than a philosopher, and his players must adapt to a completely different way of approaching matches.

Emery's reactive nature will be in evidence from the outset, as Arsenal face tests against Guardiola's City and then Maurizio Sarri's Chelsea, likely to be the Premier League's two best possession sides. This might suit Emery: they're matches where Arsenal need to play a little more cautiously and a lot more strategically than, say, at home to Cardiff. Supporters might appreciate Arsenal approaching those matches with intelligence and discipline after so many tactically underwhelming performances in recent years, particularly against the big clubs.

Realistically, though, Arsenal start a long way behind Manchester City: last season they recorded 63 points to City's 100. It's something of a familiar situation for these managers, as the last time they coached in the same league, Emery's Valencia collected 61 points and Guardiola's Barcelona 91. Emery remains the underdog, and that will be reflected in his tactical approach.