It’s hard to believe that it’s been 15 years since the first Harry Potter movie, since author J.K. Rowling’s literary creation crystallized into the form audiences followed over the course of the next decade on-screen. “Harry Potter and the Sorcerer’s Stone” director Chris Columbus deserves credit for making that experience so iconic, of course, as do actor Daniel Radcliffe and the rest of the cast, though a unique summer-night cine-concert at the Hollywood Bowl reminds just how important John Williams’ contributions were in bringing the character to life.

While an opportunity to see “Sorcerer’s Stone” with live accompaniment from the Los Angeles Philharmonic Orchestra ostensibly explains why some 18,000 fans crowded the Bowl on Wednesday night — many of them dressed in cloaks, scarves and other Hogwarts-themed accoutrements — the unique energy (some might say “magic”) felt among the crowd no doubt owed to the rare chance to revisit the fantasy franchise-starter amid under such exceptional conditions: gathered among so many like-minded admirers to see the film projected on a massive outdoor screen suspended above the arched amphitheater.

In fact, distinctive as Williams’ music is — and impressive as it is to see a full orchestra assembled to recreate it, complete with celeste, the piano-esque percussion instrument responsible for the distinctive bell-like sound of “Hedwig’s Theme” — it’s virtually impossible to listen to his wondrous score being performed without being drawn back into the film itself.

And how surreal it is to witness Radcliffe and the rest of the cast at such a young age, back when the Harry Potter series seemed so bright and kid-friendly, when the Gryffindor house colors of crimson and gold set the tone — soon to turn coal-black — and cast a vaguely Christmassy feel over the whole affair. Certainly, Williams’ music contributed to that yuletide impression (especially those celestial chimes, which can’t help but trigger subconscious flashbacks to “Dance of the Sugar Plum Fairy” from “The Nutcracker”), and though his score was succeeded by darker-sounding work by Patrick Doyle, Nicholas Hooper and Alexandre Desplat from the fourth film onward, the great “Star Wars” composer literally set the theme for the entire series.

Back in 2001, when “Sorcerer’s Stone” was originally released, director Chris Columbus’ approach seemed a bit too cheery — and maybe the music did as well. But beginning from that place made the series’ ultimate arc all the more impressive. Looking back, Radcliffe and Emma Watson and Rupert Grint seem so young, and frankly, not very good actors. But over the course of the series, their talents matured alongside their characters — and of course, each has since proven him- or herself to be edgy young performers by taking roles in works such as “Equus” and “Horns.”

This summer, audiences can see Radcliffe playing a washed-up corpse in Sundance oddity “Swiss Army Man,” and next month, he goes undercover as a skinhead in “Imperium.” Radcliffe’s child-actor past lends part of the appeal to these roles. The fact that we knew him so well (or at least thought we did) as an 11-year-old with that lightning bolt-shaped scar and round granny glasses not only gave the Harry Potter film series heft, but reinforces the subversiveness of his adult acting choices.

And of course there were all the supporting performers — those greats of British stage and screen — whose entrances earned zealous rounds of applause from the audience, especially those who have since passed on: Richard Harris and Alan Rickman. The Harry Potter series continues this fall with Warner Brothers’ adaptation of prequel novel “Fantastic Beasts and Where to Find Them,” and will no doubt find ways to carry on for decades hence, in sequels, remakes and spin-off forms. In a way, Williams’ music is the source of the series’ magic — beyond J.K. Rowling’s initial imagination, of course — and hearing it performed anew by the L.A. Phil serves to keep the enchantment alive.