Wales is gearing up for a Grand Slam showdown as Gatland's team take on Ireland in Cardiff on Saturday.
More than a quarter of a million people are expected in the capital with hopes of Wales winning this year's Six Nations title and being crowned Grand Slam champions.
Pubs across the city centre have been gearing up for the fans by stocking up on barrels.
The Owain Glyndwr pub, in St John Street, posted a photo to its Facebook account with more than 100 barrels stocked up and ready to go.
The pub said the order consisted of 127 barrels — and just under a third of it is Guinness.
The Pontcanna Inn in Catherdral Road has also stocked up, ordering in 122 barrels, which equates to around 9,920 pints.
Walkabout in St Mary Street says it expects to serve at least 11,500 pints.
Fans have travelled from all corners of the world for the hotly-anticipated game, including Paul Baker and Jon Alsop who have made the 10,000 mile journey from Australia.
Paul, who's originally from Cardiff, and Jon, originally from Barry, fly into Heathrow Airport on Friday afternoon before making the 27-hour journey back to Brisbane.
Ireland fans have been arriving in the capital since Friday.
One fan told ITV News, "It's the atmosphere, rugby passion, everything that goes with the day."
Another said, "If Wales win, it won't be the worst disaster - it's a win-win for us either way so we're looking forward to it."
Back in 2005, Wales beat Ireland 32-20 at the Principality Stadium to be crowned Grand Slam champions.
Fourteen years later and the team are hoping for a repeat of that historic weekend.
Those travelling into Cardiff have been told to prepare for strong winds and bad weather with a yellow warning in place for Wales.
Gusts of 50-60 mph are expected quite widely, with some more exposed locations seeing wind gusts of around 70 mph, mainly in coastal areas and just inland.
The Met Office is warning that heavy and persistent rain is expected to affect Wales through Saturday, with the potential for flooding.
Despite the weather, the Principality Stadium roof will be open for the game. Wales' preference was for the roof to be closed, but Ireland requested it remained open.
Fans have been told to allow plenty of time to get to the Principality Stadium - with road closures and long queues expected on Saturday.
Train bosses have warned people could be waiting for up to 90 minutes at Cardiff Central on match day and roads surrounding the city centre will be closed between 11:15am and 5:45pm.
Kick off is at 2:45pm.
Ahead of the Six Nations opener back in February, Gareth 'Alfie' Thomas gave his predictions about Wales' performance in the tournament - and his theory has proved to be right so far: