I get asked that with some frequency. And I've got an answer at the ready: Bruce Springsteen and the E Street Band. Dec. 9, 1980. At the Spectrum.

At the time, the reasons didn't have much to do with the setting. It was just another sports arena, a cavernous, concrete slab of a building shaped like a giant tuna can that, besides being the home of the Sixers and Flyers, became the iconic venue in Philadelphia for bands that could pull in close to 20,000 people a night.

That December night in 1980 was special because the night before - when Springsteen had also played there - John Lennon was killed. So on the ninth, the expectation was that the Boss would take the advice of his guitar-slinging consigliere, Steve Van Zandt, and the show would not go on.

But go on it did, with Springsteen coming out and explaining to the assembled faithful, including my brother, Nick, and me, that "it's a hard world that asks you live with a lot of things that are unlivable. And it's hard to come out here and play tonight, but there's nothing else to do."

Then he played "Born to Run." And four hours later, after performing with more life-affirming determination than I've seen anyone equal before or since, he played "Twist and Shout" as one final tribute to Lennon.

The magic in that mythic night wasn't created by the Spectrum itself. It could have happened anywhere, I suppose. But the legendary ardor of the Philadelphia rock audience added to the excitement in the room and the momentousness of the occasion.

I saw a lot of lousy shows at the Spectrum, too. Milli Vanilli comes to mind, though watching those dreadlocked, lip-synching Germans break-dance in their bicycle pants was not without its entertainment value.

Over the years, the Spectrum became something more than just another sports arena. "Politicians, ugly buildings and whores all get respectable if they last long enough," John Huston's character, Noah Cross, says in the movie Chinatown.

The Spectrum came into being in 1967, at the dawn of the modern rock concert era, just a year after the Beatles played their last show at Shea Stadium. And while it isn't any uglier than the other arenas of its time, it took on an air of respectability as it grew older.

The Spectrum was the place where Philadelphia music fans convened on a grand scale, to see their heroes in the flesh, and get a contact high in the bargain.

Local bookers Electric Factory Concerts brought in all of the cornerstone acts of the classic rock era. In July 1972, the Rolling Stones played two nights on their tour for Exile on Main Street, with Stevie Wonder as the opening act. The next June, Springsteen opened for Chicago, playing his first of 30 shows in the building. (That puts him second on the Spectrum performance list, behind the Grateful Dead with 53.)

In the '80s and '90s, illustrious acts like Guns N' Roses and Rage Against the Machine played the Spectrum. But so did cheesy acts like Styx - which I saw of my own free will when I was 16.

Trip McClatchy, 50, of Havertown, who blogs about music at teenkicks.blogspot.com, saw James Taylor there in 1972, the first of McClatchy's 76 Spectrum shows. (He has them on an Excel spreadsheet.) He ranks the Faces with Rod Stewart in 1973 second to Springsteen. But he also remembers seeing Slade, Jo Jo Gunne and Brownsville Station in 1974, and taking his younger brother Kevin to see Kansas in 1977, only to have him sleep through the show except for "Carry On Wayward Son." (I've got my own embarrassing tale of sleeping through a Springsteen show my brother took me to in July 1981, but that's another story.)

As a music venue, the Spectrum started to look good in 1996, the year that the spiffier, more capacious building then called the CoreStates Center (now the Wachovia Center) opened. The next generation arena had all the amenities - more bathrooms, larger concourses, and, of course, lots of corporate luxury boxes to generate income for those Sixers and Flyers salaries.

But all the room those boxes take up means that second-deck music fans are much farther away from Faith Hill or Mary J. Blige, and more likely to need video screens for an up-close view of their idols.

Music fans notice the difference, and so do the bands. When acts like the Cure, who played the Spectrum in June, wind up in the old arena (usually from a scheduling conflict at the new one), it gives a show an added buzz - and arguably, a slightly better sound mix - even if it means spending more time in the bathroom line.

"The old building has more of a feeling of a dive bar, and less of a country club," says McClatchy.

Former Phish front man Trey Anastasio, who grew up in Princeton, said in an e-mail yesterday that he would miss the Spectrum "deeply. I saw my first arena rock and roll show there - (Pink Floyd, Dark Side of the Moon). . . . I was also fortunate to have the opportunity to perform there a dozen or so times as a member of Phish. Those shows were as exciting and memorable for me as any I ever performed. I just loved everything about the place.

"The folks who own the Spectrum extended numerous invitations for us to play in the Wachovia Center, but I said I didn't want to leave the Spectrum until the Flyers won the Cup again. I guess now I'll have to reconsider - assuming, of course, that I'm ever invited back!"

Now, the Spectrum's days are numbered. I'll miss it, and not just because there were some great shows there back in the day - I'm sorry there won't be more great ones to come. And when the old arena is demolished, an essential piece of Philadelphia music history will go down with it.

at 215-865-5628 or ddeluca@phillynews.com.

Read his blog, "In the Mix," at http://go.philly.com/inthemix.