This is rugby's day of reckoning, and it can make or break the game. But why is it a big deal?

"You could hear them chanting 'Lions'," the Wallabies great said. "It was pretty intimidating in your own country."

You'll hear it again in Brisbane on Saturday night, where pints of Guinness will be poured into a sea of red on Caxton Street as thousands of touring British and Irish Lions fans make their way to the opening Test of a three-match series against the Wallabies.

Crowd records are being shattered at will. A new benchmark has been set in Adelaide. The Western Force had to shift across town to accommodate the largest home crowd in club history.

The ACT Brumbies played in front of their biggest home crowd in 20 years. Full houses await during Tests in Brisbane, Melbourne and Sydney.

Outside of a World Cup, a British and Irish Lions tour is rugby's greatest spectacle. They arrive on these shores every 12 years, meaning for most players, it's a once-in-a-lifetime opportunity.

Unless of course, your name happens to be George Smith. He remains the only Wallaby to have played the Lions in two separate series. James Slipper is about to join that elite club, and so too could James O'Connor following his fairytale recall.

But why is this such a big deal? An all-star cast including Wallabies greats Matt Giteau, George Gregan, Owen Finegan, Joe Roff and Justin Harrison, former Lions centre Jamie Roberts, and commentator Sean Maloney tell us why.

Cast an eye over Roberts' resume and you'll find 94 caps for Wales, three Six Nations titles, two Lions tours and a 2009 Lions player of the series award. So when he starts talking about what it means to represent a team boasting the best of England, Wales, Ireland and Scotland, you listen.

"It's an amazing thing, the Lions tour. For British and Irish players, it's the pinnacle of what you can achieve in the game, to get selected on that tour," Roberts said.

"There's also a respect for the host countries and the fact it's once every 12 years for them. For us players, it was once every four years and we were very privileged to play in one. Some legends of the game have played in five.

"The Lions, above any other rugby institution in the world, they connect with their history better than anyone. One of the strengths of that brand is connecting with its history, and as a player, you're very well aware of the people who have been before you and the legacy you want to leave in the jersey.

"As a player, that weighed heavy on me, certainly when I played, you want to wear that jersey. For the first time, you're in a position where you feel very empowered by it."

Gregan remembers his shot at the Lions all too well. The embarrassment of being "caught with our pants down" in Brisbane before finding themselves on the ropes in Melbourne.

Then Roff caught fire in the second half, and Harrison did his part in Sydney. The rest is history - and you get the sense he'll never tire of being asked about it.

"You might never play them in your career, and you might play over 100 Test matches," Gregan said.

"The likes of Matt Giteau never played the Lions, Nathan Sharpe, these are centurion Wallabies and great Wallaby players who never got the chance to play against the British and Irish Lions.

"If you're lucky enough - it doesn't matter if it's provincial or international - to play against them, you're very fortunate."

Roff is asked about the 2001 series win over the Lions more than anything else in his career.

"You don't realise how special it is until you're reflecting on your own career and there's the nostalgia," Roff said.

"But it was such a special series that realistically it came down to the last play of the last Test in front of a packed stadium in Sydney."

Ask Roberts about his Lions debut and he takes you to "the deepest, darkest place in South Africa in a little place called Rustenburg".

The Royal Bafokeng Sports Palace almost felt deserted. Little more than 12,000 people filed into the 42,000-seat venue, with 55,000 people a little further down the road to watch the Bulls pile 61 points on the Chiefs to win a Super Rugby title in Pretoria on the same day.

"You contrast that with the first Test in Durban in 2009, that was unlike anything I'd experienced in my life. You come out of the tunnel and you see all red," Roberts said.

"It makes you realise how much people have invested in the Lions. They save their money and pay a small fortune to fly to the other side of the world to support you.

"That sense of privilege, that position you're in, you respect that and you respect what you're doing for the fans. It's so unique in world sport, bearing in mind, three or months prior they're going at each other and heckling each other in the stands at a Six Nations."

But now, Gregan expects they'll have "half the stadium barracking for them in every Test match". Which is why, every now and then, commentator Sean Maloney will just put the microphone down.

"That 'Lions, Lions, Lions' chant - it's so stupidly simple, but it's so effective and so awesome in its delivery, you just let that carry. It's really special," Maloney said.

"By the time we hit that first Test in Brisbane, I reckon it's going to be bigger than it was in 2013. In terms of interest, fans, noise, and energy around the game, I reckon it's going to be off the hook.

"It's bringing back a lot of people to the game who may have drifted off in the last little bit. You're seeing a lot more faces, you're seeing more of those old school Wallabies jerseys that have been washed out, the old school Vodafone ones, even the old school Reebok ones are popping up.

"Sprinkle in all the Lions fans too, they're incredible, mate. I cannot believe they're still upright by the time we hit kick-off, because I see them in the pubs beforehand, and they're going hard. They've got the goad to last until full-time. It's amazing."

Harrison was "petrified". Imagine being thrown into a series decider for your Test debut, when you've already been cast as the man the Lions love to hate?

A bitter feud with Austin Healey had erupted during Australia A's victory over the Lions in Gosford 24 years ago, before the Englishman scored a match-winner during the tourists' last-gasp win over Harrison's Brumbies.

Soon labelled a "plod", "plank" and an "ape" by Healey in a newspaper column, Harrison was called in for his Test debut and came up with a famous lineout steal to clinch a series victory.

"I probably should have retired after that," Harrison said. "I think it's important. It is a bit of a pantomime sport, right? There are villains and heroes and characters in the sport. Austin was one of them, absolutely.

"It gives you a plot. I've had a lot of people come up and remind me that Austin's hard to ignore but worth the effort, so I didn't use it as any extra motivation or typically spend any more time on it.

"We'd had a love affair since the Australia A fixture in Gosford and became quite known to each other."

The touring villain this year? Lions rookie Henry Pollock has channelled Australian cricket great Glenn McGrath's famous Ashes predictions by declaring his intention to whitewash the Wallabies and become the best touring team ever.

"We want to come here and be the best Lions team ever," Pollock said. "We've been talking about that loads, and 3-0 is definitely on the table. Hopefully, we can achieve that."

Giteau figures there is no ceiling on just how good Joseph-Aukuso Suaalii can be.

Which is saying something about the Wallabies' marquee man, the marketable superstar Rugby Australia bosses are investing $5 million in to help change the face of the code in this country. With the price tag comes pressure.

But just like Mat Rogers, Lote Tuqiri and Wendell Sailor before him - the Wallabies' back three in the 2003 World Cup final - Giteau expects the game's latest big-name NRL convert to thrive.

"There's no real cap on how good he can be, he just needs time in the saddle. The hardest thing for Joseph is he came across on his own.

"Whereas your Lote, Wendell, Matty Rogers, all kind of came around the same time to share the pressure and the burden of being that big superstar. He's had to carry that on his own," Giteau said.

"Everyone expects huge things. This isn't just under 8s, when you can just give him the ball and he'll score, but you can just see the value he adds, the way he competes, defensively the reads he makes, and how valuable he is when he's got time with the ball.

"We've just got to be patient. He's growing, each week you can see he's getting better and better."

If you're looking for a Lion to wreak havoc, Roberts points to two men - captain Maro Itoje and flyhalf Finn Russell.

"Obviously the captain, I think Maro has a lot of pressure on him. Recent history has told us this guy takes his performances to another level when the pressure is at its highest," Roberts said.

"He's an incredible role model for our game, and above all else, his performance level for the past two seasons has been unparalleled.

"He's an unbelievable rugby player, he's a nine out of 10 performance every time he plays the game.

"And Finn Russell, an absolute rockstar player. There's a lot of hope on his shoulders. As a fan, when you watch this guy play, he has had an incredible season domestically, and with Scotland.

"At the minute he walks into the 10 jersey for the Lions, and that position and responsibility in the playmaker's jersey is huge. I fully expect him to deliver."

History tells us the series will come down to the finest of moments, like a Kurtley Beale slip or a Harrison steal.

Touring scribes might tell you Australian rugby is weak. After all, the Wallabies only just snuck home against Fiji in their only Test before the Lions series.

But then again, the tourists were beaten by Argentina before they left Dublin - although they now have the benefit of five games together on these shores, having swept all before them.

"Every time the Lions have come here, it's been 1-1 going into the third game, so I hope to see the same," Finegan said.

"It's a Wallaby team that's improving, they beat England and pushed Ireland to the edge and almost got another victory. In both of those games, they were a minute or two from winning or losing. I imagine this series will be much the same.

"It will be tight all the way in. The advantage the Lions get going into the first Test is they've got some consistency of football, they've built some combinations, and the Wallabies have had one warm-up against Fiji.

"We all hope it's 1-1 going into the last game, and we'll be cheering for the Wallabies going into the third Test."

Wallabies "psycho" Nick Champion de Crespigny has been thrust into a shock debut in the British & Irish Lions opener as coach Joe Schmidt plots a Brisbane boilover.

The Canberra Grammar graduate will be one of just two uncapped players in the 36-strong squad, surged into calculations after injury to pivotal backrower Rob Valetini and the in-form Langi Gleeson.

Hulking lock Will Skelton, who missed the Fiji Test with a calf niggle, also failed to prove his fitness.

Schmidt said all three were tight calls and he expects them to be fit to play in Melbourne next week's second Test.

Canberra-raised Champion de Crespigny returned from a Top 14 stint with Castres Olympique to play for the Western Force this season to join the back of a bulging queue of contenders.

But, with two-time defending John Eales Medallist Valetini and Gleeson on ice - former captain Liam Wright (shoulder) is also out of the picture - he'll be asked to dent a Lions line that has enjoyed five relatively comfortable wins since arriving in the country late last month.

"Big shoes to fill," Schmidt said of the debutant, who brings an aerial threat at lineouts and starch on either side of the ball.

"He was on the radar (12 months ago). Not necessarily right in the middle, but in the periphery and got a little bit closer as the season wound on."

Backrower partner Fraser McReight was less diplomatic. "He's a psycho; loves contact and ready to go," the No.7 said.

"Loves the physical nature of the game. I've heard all the stories from the Force boys."

The coach also backed "quietly confident" 22-year-old Tom Lynagh to steer the ship in a new-look halves combination with Jake Gordon.

Ben Donaldson will provide backline back-up on the bench, with Schmidt resisting the temptation to recall veteran James O'Connor, who wore the No.10 in all three Tests 12 years ago.

Hooker Matt Faessler returns after a last-start hat-trick in gold, having started for the Reds instead of playing against Fiji in his comeback from a hamstring injury.

Andrew Kellaway has bumped Filipo Daugunu off a new-look bench that includes hooker Billy Pollard, scrumhalf Tate McDermott, prop Tom Robertson and flankers Tom Hooper and Carlo Tizzano.

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James Slipper will join George Smith as the only Wallabies to feature in back-to-back Lions series in the professional era while No.8 Harry Wilson has retained the captaincy.

Lynagh hasn't played since the Reds lost their Super Rugby quarter-final in early June, with a broken hand ruling him out of the Fiji Test.

The Italy-born, England-raised playmaker finished school and moved to Australia in 2021 and has flourished under Wallabies coach-in-waiting Les Kiss as the Queensland Reds' main man for the last two years.

He'll make Australia rugby history as the first father-son Wallabies to face the Lions after Michael Lynagh wore the No.10 against the Lions in 1989.

WALLABIES: 1. James Slipper, 2. Matt Faessler, 3. Allan Alaalatoa, 4. Nick Frost, 5. Jeremy Williams, 6. Nick Champion de Crespigny, 7. Fraser McReight, 8. Harry Wilson (c), 9. Jake Gordon, 10. Tom Lynagh, 11. Harry Potter, 12. Len Ikitau, 13. Joseph-Aukuso Suaalii, 14. Max Jorgensen, 15. Tom Wright. Reserves: 16. Billy Pollard, 17. Angus Bell, 18. Tom Robertson, 19. Tom Hooper, 20. Carlo Tizzano, 21. Tate McDermott, 22. Ben Donaldson, 23. Andrew Kellaway.