As two of the so-called “Big Four” bands of thrash metal, Anthrax and Slayer have a long and loud history together. So it only made sense that the former would join the latter for their retirement tour.

As it turns out, Anthrax agreed to come along for the ride before they even knew it would be the last one of Slayer’s career.

“We’re very close, good friends with Slayer, for forever. … I’d heard rumors about it and I’d talked to the guys about it, and they said, ‘Yeah, soon, soon, soon.’ And after we were booked, that’s when we found out it was the farewell tour,” Anthrax bassist Frank Bello said in a phone call from the tour bus on the way to Dallas. “And that made it all even deeper, in a sense, for us, because of course you wanna see your buddies out and be there with them the whole time. We’ve toured with Slayer a whole lot in our careers. And just to be here right now is really special, because you see the impact that they’ve left on people.”

“The Final World Tour,” which also includes Lamb of God, Testament and Napalm Death, visits USANA Amphitheatre in West Valley City this Sunday.

(Photo courtesy of Anthrax) Frank Bello, front, and Anthrax, shown performing at the 02 Forum in Kentish Town, London, on Feb. 10, 2017, will visit USANA Amphitheatre in West Valley City on Sunday, Aug. 19, in support of Slayer.

While Bello said the two bands had enough crazy moments together over the years that “I could write a book on those stories,” he didn’t hesitate when asked if he had a personal favorite.

“We’re in the dressing room, the guys in the bands and the crew guys all hanging out, and the shots of Jägermeister start going. It never really ends. One time in Europe, I remember specifically, the party carried over into their tour bus. I didn’t know this at the time, I’d heard a rumor, but there was a frozen Jägermeister machine in their tour bus. And that was the ruination of me!” Bello said with a laugh. “That night, I puked everywhere — from their tour bus, there was a trail to my tour bus, and continuing in my bathroom in my tour bus. I remember waking up, and I was hugging the bowl, and it was 7 a.m., I think, and I was still puking. It was one of those really horrible hangovers. And it was a show day, by the way. I didn’t realize we had a show that day, and I paid for it dearly, with a great hangover. The Jägermeister on the tour bus — very dangerous!”

Of course, the retirement of one legendary speed-metal outfit has naturally led to questions about whether Bello and his Anthrax bandmates have begun to consider their own musical mortality. The band, after all, was formed in Queens back in 1981. And there’s been no shortage of lineup turnover throughout the years, though Bello (who started as a roadie and took over for founding bassist Dan Lilker in ’84) has been one of the group’s constants over that time, along with rhythm guitarist Scott Ian and drummer Charlie Benante.

Still, he doesn’t see the band’s finish line on the horizon. If anything, he said, this decade has actually sparked renewed interest in Anthrax from music fans.

The Big Four — Anthrax, Slayer, Megadeth and Metallica — joined forces on the same bill for the first time ever in 2010, with seven performances at the Sonisphere Festival across Europe proving enormously popular. Furthermore, the return of longtime singer Joey Belladonna helped make the group’s two most recent albums (2011’s “Worship Music” and 2016’s “For All Kings”) their highest-charting debuts ever. (The band also released a live DVD, “Kings Among Scotland,” on April 27 this year.)

“There’s been, like, this rebirth of people noticing the band … and it makes you hungrier,” Bello said, his staccato accent picking up speed. “This is a very, very hungry band, Anthrax. Maybe it’s our New York mentality; I don’t know what it is, but there’s a very fierce energy going on within the band. We can’t wait to see what’s next. So, if anything, we’re just getting started, I think. There’s a whole new generation of kids and fans coming out. I think our fanbase is growing big-time.”

Part of what’s next is another album. Bello said they were supposed to be writing a record right now, “but this Slayer tour came up, and you can’t say no to this, because of the obvious reasons.” So instead, the group will convene in January to start the songwriting process.

He said he’s expecting something of a shift in the tone of the new material.

“We’re gonna go heavy — heavier than ever, I think,” Bello said. “That’s just the vibe. There’s an inner anger, which I think is great for songwriting.”

That said, he doesn’t want brutality at the expense of musicality. This is, after all, a man who cited The Beatles’ “Revolver” and U2’s “The Joshua Tree” as two of his all-time favorite albums. “I just wanna hear melody with my music,” he said. “… Anthrax has always been a melodic metal band.”

And so it becomes a matter of trying to strike the right balance between heavy riffs, melodiousness and standout vocal performances. In that respect, Bello said, they are copying the template established by metal icons such as Black Sabbath, Iron Maiden and Judas Priest — “That’s what we grew up on, so why not just follow through with that?” — while trying to put Anthrax’s unique spin on the formula.

(Photo courtesy of Andy Buchanan) Anthrax (from left: Joey Belladonna, Frank Bello, Jonathan Donais, Charlie Benante, Scott Ian) perform at the Barrowland Ballroom in Glasgow, Scotland, on Feb. 15, 2017.

“It’s not your generic metal, let’s face it. We care about our songs. It’s not just that we need to put out a record, we need to put out the record. It’s about living with these songs — that’s why it takes us a while to write,” he said. “It’s about songwriting, man. It really is. It’s about every little nook and cranny on that song. Anthrax has never phoned anything in, and I don’t see us ever doing that.”

The same applies to their live performances.

“Nah, dude — can’t do that. It’s not in our makeup. It’s not in our DNA,” Bello said. “We genuinely love playing together. We’ve been doing it for so long. But that energy you create that’s between you and the audience, that’s the drug that you can’t do without.”

Jäger, though, might be a close second.

“I’ve fallen out of a lot of bars in Utah!” Bello conceded with a chuckle. “There’s a great metal fanbase there. We look forward to it. We try to bring the party wherever we are. We want people to have a good time — come to the show, forget about your issues. And again, it’s the Slayer farewell tour, so we’re all tipping our hats to them and just supporting them and having a great time. The great thing about this tour, that all metal fans in Utah should see, is metal is alive and well.”

And maybe a bit hung over, too.

Slayer
With Lamb of God, Anthrax, Testament, Napalm Death
When • Sunday; doors at 4 p.m., show at 5
Where • USANA Amphitheatre, 5150 Upper Ridge Road, West Valley City
Tickets • $29.50-$85; Smith’s Tix