PHILADELPHIA – It all started with a book discovered by former Philadelphia Eagles fullback Owen Schmitt.

The subject: The Berserkers, a group of Norsemen who were said to fight with an animalistic ferocity. Schmitt told his teammates about them, particularly the offensive linemen. Next thing you knew, as Pete Townshend once wrote, the beards had all grown longer overnight. Right tackle Todd Herremans sported a Berserker-inspired topknot for a little while there.

What's behind the beards on Jason Kelce and the Eagles? Well, have you heard of the Berserkers? AP Photo/Brian Garfinkel

With the Eagles going to the land of those other Vikings – they play in Minnesota on Sunday – center Jason Kelce was quick to make the distinction. He and his hirsute linemates are not emulating mere Vikings here.

“Owen lent me the book about the Berserkers,” Kelce said. “We both got all fired up. That was two years ago. I decided to do it again this year. It will stay on against the Vikings – Vikings meet Vikings.”

Kelce may have to buy a copy of that book for coach Chip Kelly. On Tuesday, when the Eagles practiced in their indoor facility, the usual loud music was augmented by the Viking horn that blares relentlessly in the Metrodome. That was news to Kelly.

“I have no idea what that is,” Kelly said. “I literally have nothing to do with the music. I thought it was the horn from 'Anchorman.' Remember when he asked for his guys and they were all standing right next to him? I went conch shell.”

Conch shell? It’s a Gjallarhorn, and it’s safe to say Kelly will be very familiar with it by the end of Sunday’s game. It will be music to the ears of the Berserkers on his offensive line, though.

Left tackle Jason Peters and left guard Evan Mathis have substantial beards. Herremans, now at right guard, shaved his beard off and then regrew it for Movember. It’s relatively tame compared with the other four guys. Rookie right tackle Lane Johnson has succumbed to the peer pressure, it seems, and his beard is increasingly bushy.

“We didn’t say anything to him about that,” Herremans said.

It turns out Johnson has a very different reason for his beard.

“I’ve always had facial hair,” Johnson said. “When you gain a bunch of weight, you kind of have a double chin. So it covers that up. You will never see me with this gone.”

So no Norse warriors?

“That’s Jason’s inspiration,” Johnson said. “Go ask him about the Berserkers. That’s all he talks about.”