When Wales recovered from a record half-time deficit to beat France in their opening match of the 2019 Six Nations in Paris, then head coach Warren Gatland said his team had "forgotten how to lose".

Gatland led his side to the World Cup semi-finals later that year but, as is often the case in Welsh rugby, after highs there soon followed lows.

Just 12 months after Gatland's glittering 12-year reign had ended, under his successor, Wayne Pivac, Wales found themselves picking the bones out of their worst Six Nations for more than a decade.

With seven defeats from 10 matches, Wales had suddenly remembered how to lose.

And yet now, three months on from a dismal 2020, Welsh rugby's never-ending cycle of feast and famine has swung back to the opposite extreme.

Wales return to Paris on Saturday, one win away from the most improbable of Grand Slams.

It would be their fifth of the Six Nations era - more than any other country - but those peaks have been punctuated by dire troughs, with Wales finishing in the bottom half of the table 12 times out of 21 since the competition changed from five to six teams.

As Pivac says, this year and the last have been like "chalk and cheese" for Wales and, as history tells us, this is the boom and bust nature of Welsh rugby.

Wales spent the 1980s and 1990s in the wilderness; long, barren decades which yielded just two Five Nations titles, one of which was shared with France.

Such fallow years would have been dispiriting for most but they cut deeper for Wales, a rugby nation built on the mythology of a bygone golden era, the 1970s of seven Championships, three Grand Slams and a generation of players who redefined their sport.

Those faded glories felt like fantasy at the beginning of this century, with Wales failing to finish higher than fourth in the first five editions of the Six Nations and lumbered with the wooden spoon in 2003.

But late in 2004, there was just a hint of recovery with encouraging performances in narrow defeats by South Africa and New Zealand.

"I think that New Zealand game allowed us to actually realise that we could mix it with the best, that we could perform against the best team in the world," says Tom Shanklin, the former centre and wing who scored one of Wales' tries in their 26-25 loss to the All Blacks.

"We took a lot of confidence from that."

Wales started the 2005 Six Nations at home against England three months later. They had not beaten the world champions since 1999 but overcame their neighbours with a nerve-shredding 11-9 triumph.

"You could take a bit of confidence from losses but nothing like winning a game, and it only takes one game to kickstart that momentum," says Shanklin.

Wales discovered as much as their victory over England lit the touch paper for a thrilling revival. After high-scoring wins in Italy, France and Scotland, Wales returned to the Millennium Stadium to face Ireland on the final weekend.

Cardiff was bathed in unseasonably warm March sunshine as Wales stormed to victory, bringing home their first Grand Slam since 1978 to start an almighty party.

"We won a first Grand Slam in 27 years but that came with a bit of a hangover," says Shanklin.

"I think we thought that we were just going to crack on and become world beaters. It doesn't quite work like that.

"Rugby is constantly evolving, you have to evolve with it, and we didn't."

As a result, Wales' title defence in 2006 was a shambles.

Head coach Mike Ruddock resigned just two games into the campaign as controversy raged about alleged power struggles between the players and staff.

Wales finished fifth in the Six Nations table with only one win from five matches, and they suffered the same ignominy under Gareth Jenkins the following year.

Later in 2007 came the ultimate embarrassment as Wales were dumped out of the World Cup in the group stage after losing to Fiji.

Jenkins was sacked in a car park and, just two years on from winning a Grand Slam in such glorious, cathartic fashion, Wales were a laughing stock.

"We weren't in a great state," says Shanklin, one of those who had started each of the Grand Slam matches as well as the humbling by Fiji.

"As a group, confidence was low. We also knew that we still had quality players around us."

Enter Gatland.

The New Zealander had been a serial winner as Wasps coach and he recognised what Shanklin saw: that Wales had the raw materials to be a good side.

Gatland told his new charges that they could be successful again, but there would need to be a change from the carefree style which had brought them the 2005 Grand Slam but also the damaging defeats which followed.

"The biggest thing that we took from Warren Gatland coming in was an identity, a style of play that suited something that we possibly didn't have previously," says Shanklin.

"It was back to basics, working harder than the opposition. It wasn't going to be expansive but play to your personnel.

"Warren came in and gave us a blueprint of how he wanted us to play the game."

It worked. In Gatland's first game in charge in February 2008, Wales beat England at Twickenham for the first time in 20 years.

Home victories against Scotland and Italy followed, before a narrow win in Ireland set up a Grand Slam-clinching triumph over France in Cardiff.

From the elation of 2005 to the humiliation of 2006 and 2007, within months Wales had picked themselves up from one of their lowest ebbs to seal a stunning transformation.

"That's where Wales are just the greatest. When everyone writes Wales off, they spring a surprise and come out of the blocks," says Shanklin, who played in all five games of the 2008 campaign.

"A lot of the time, it's either we'll win a Grand Slam or top the Championship, or we finish bottom.

"We're all or nothing."

Gatland's first Six Nations with Wales produced a Grand Slam and so did his last in 2019. Another clean sweep in 2012 and a Championship one year later made his 12-year reign the longest and most successful in Welsh history.

Even if he was not immune to the fluctuations and internal dramas of Welsh rugby, the arch pragmatist instilled in his side a level of consistency which had been missing under his predecessors.

Whereas the 2005 Grand Slam was Wales' only top-half finish in the Six Nations before Gatland's arrival, they were third or higher in eight of the New Zealander's 12 campaigns.

As Gatland contemplated the end of his tenure after narrowly losing a 2019 World Cup semi-final to eventual champions South Africa, he said it would "break his heart" if Wales "went back to the doldrums".

The comment was vintage Gatland, reflecting on his stellar achievements with Wales but still finding time to apply a little pressure on his successor. A coach with a fondness for playing mind games with opponents, Gatland now seemed to be gently turning the heat on Pivac before his compatriot had even started.

Pivac was inheriting a team who had enjoyed historic success but had also endured criticism for their style of play under Gatland, whose functional and abrasive approach had been dubbed 'Warrenball' by his detractors.

Gatland bristled at the moniker, and it represented an ethos from which Pivac wanted to gradually move away as he sought to sharpen Wales' attack and evolve their game to a level where they could close the gap on the southern hemisphere heavyweights.

However, Pivac's early attempts at progression initially looked like severe regression.

Wales beat Italy 42-0 in his first Test in charge but followed that with six successive defeats.

Criticism mounted from fans and pundits, while Pivac had to answer questions about his job security last November, just 12 months into his four-year contract.

Wales were not attacking with the verve many had expected under the former Scarlets coach, while the team lacked the robustness which had been a hallmark of Gatland's reign. Wales' set-piece was a mess and they had become so porous that defence coach Byron Hayward swiftly departed.

A year after being top of the world rankings, Wales had plummeted to ninth having lost seven of their 10 matches in 2020. A fifth-place finish in the Six Nations was their worst since 2007, while their only wins in the year came against Italy and Georgia.

Pivac and his staff insisted they were not panicking. They said the autumn was about developing strength in depth and, despite the concerning results, they demonstrated their commitment to building for the future by handing debuts to 11 players during their first year in charge.

"Like every team, we needed time to bring new boys in and after the World Cup it was an excellent chance to do that," says George North, Wales' wing and centre.

"Last year was a chance to give those younger and newer players a chance to get some experience of international rugby and prepare the squad to get to where we are now.

"That's rugby at this level. You have to go through those periods."

While Wales endured a chastening autumn, North had to overcome a difficult spell of his own as he was left out of the team.

It was a striking decision from Pivac to drop the British and Irish Lions player but one which had the desired effect, with North rediscovering his form with Ospreys before returning to the international set-up rejuvenated.

Having moved from wing to outside centre, the 28-year-old has been one of Wales' best players in this Six Nations, during which he has become the youngest player in the world to pass 100 caps for his country.

North's transformation over the past few months has mirrored Wales' in some respects, and his centre partner Jonathan Davies likens the team's improvement to that of the Scarlets side he played for under Pivac.

"When I came back to the Scarlets [in 2016] it took a while for us to find our feet. We might have lost our first three or four games with Wayne in charge," says Davies.

"But by the end of the season we were playing some of the best rugby I've ever been involved in.

"The autumn was when we [Wales] could lay foundations and we knew then, coming into the Six Nations, that was an opportunity to springboard our performances and make sure we're competing.

"Although results weren't what we wanted, we took positives from it and we're reaping the rewards from it at the moment."

The mantra is clear. Speaking to various members of the Wales squad, you get the impression that the players buy into Pivac's vision. They grasped the long-term purpose of their efforts during a difficult autumn, and now they are enjoying the fruits of their labour.

Another who has played under Pivac for Wales and Scarlets is fly-half Rhys Patchell, absent from this Six Nations because of injury.

"Wayne is very good at creating an environment where the boys feel that they are driving it," he said before last month's win over England.

"Once you gain a bit of momentum, he's very good at capitalising on that momentum and then it almost becomes a self-fulfilling prophecy.

"I feel that's a real strength Wayne had at the Scarlets, where we won the league in unbelievable fashion and went to a semi-final in Europe.

"It was almost like once the fire was lit and the momentum was with the team, he just fanned it and kept it going and the boys really thrived on that."

There is that word again: momentum.

The material improvements Wales have made over the course of the Six Nations have been clear. They have fixed their line-out, tightened their defence and, as captain Alun Wyn Jones has noted, have become more clinical in attack.

There are numerous other facets of the game which the coaches and players have fine-tuned as the competition has progressed - not that they have wanted to divulge the finer details this week and show their hand to France before Saturday's match.

But as well as those tangible qualities, there are the intangibles too.

This Wales team, the most experienced in the country's history, have long demonstrated their resilience under pressure, their ability to fight back from adversity and to close out tight games at pivotal moments.

And as was the case in 2019, 2012, 2008 and 2005, this year's Six Nations has shown how powerful an intangible quality momentum can be.

Having helped drive that motion in 2005 and 2008, Shanklin sees history repeating once again.

"Momentum. I think that's the big thing that's changed with Wales," he says.

"Who would have thought we'd be in this position right now?

"I honestly believe playing your home games at the Principality Stadium is a big factor. You look at the Autumn Nations Cup and it was played at Parc Y Scarlets. That's not home to Welsh rugby.

"Without the fans, I think you need all the positives you can get. And I certainly think that is a massive factor in the mindset going out to play.

"I think defensively we've been rock solid. So it's an all-round improvement I see, from the attack side of creating opportunities, finishing opportunities, and defensively as well.

"But the main thing is just momentum. We've seen previously how that has affected Wales, and all of a sudden now we seem to be riding that wave.

"At the start of the Six Nations I thought there's absolutely no chance we'd be going for a Grand Slam."

Shanklin was not the only one who held that view. Surveying the destruction at the end of last year, it was difficult not to be downbeat about Wales' prospects.

But as they did in 2008, when they hauled themselves off the canvass after their World Cup debacle just months earlier, Wales have made an instant - and potentially spectacular - recovery.

"We seem to perform best when our backs are against the wall, when the pressure is on, when no-one expects us to win," Shanklin adds.

Wales had forgotten how to lose when they were in France two years ago. They have since rediscovered the habit and beaten it all over again.

Now they are back in Paris, Wales, as ever, are all or nothing.