Imagine a music world without boundaries, where Beethoven collaborates with Led Zeppelin, Mozart with Elton John and Puccini with the Beatles.

Imagine no more as “Rocktopia” unites classical compositions with classic rock songs when it plays three northeast Ohio concerts.

“I wanted to draft a real mash-up that merges the two not just a snippet here, a snippet there,” said Randall Craig Fleischer, co-creator of “Rocktopia” and music director and conductor of the Youngstown Symphony Orchestra.

“What ‘Rocktopia’ is is opera, symphony and classic rock in a mash-up that really rolls itself out like a scene from an opera or a movement from a symphony. What makes opera and a symphony work in terms of the structure is the dramatic conflict between themes and melodies.”

The Canton native offers a couple examples of this approach. “I was looking at classical music and rock ‘n’ roll songs where the meaning overlapped. Once I had that identified, there were certain things like the aria ‘Quando m’en vo’ from ‘La Boheme,’ melodically it fits so perfectly with ‘Something’ by the Beatles. That one was both dramatic, the subtexts overlapped, and the melodies fit perfectly.

“With ‘Stairway to Heaven,’ I immediately thought of the slow movements from Beethoven’s Symphony No. 7 in part because the emotionality of both pieces fit and in part because they’re both in A minor. So, there were those mechanical musical considerations but, mostly, it was content to content, pathos to pathos, not like ‘Oh, these melodies would fit on top of each other.'”

His interest in fusing rock with classical began when he was a teenager.

“I often say that I tried to create my first rock fusion arrangement when I was 14 years old. It was an arrangement for a rock band, the overture to Handel’s ‘Messiah.’ It’s always been a passion of mine and I’ve done all kinds of projects along the way.”

That includes working outside the classical realm with John Densmore (The Doors), Natalie Merchant, Blondie, Ani DiFranco, John Cale (Velvet Underground) Garth Hudson (The Band), Kenny Rogers, Chris Barron (Spin Doctors) and R. Carlos Nakai.

Merging the two musical styles not only made perfect sense but Fleischer also saw popular rock artists of the late 1960s / early ’70s attempt to blend the two genres. As rock stretched the boundaries of its blues and country roots, artists such as Emerson, Lake & Palmer transformed classical pieces to the rock ‘n’ roll domain while Deep Purple and the Moody Blues recorded with symphonies.

“Those things had an influence on me but I’m really primarily a classical musician. I grew up with Casey Kasem’s ‘American Top 40’ and I love rock ‘n’ roll. It always struck me as ridiculous that the world of classical music didn’t embrace rock ‘n’ roll and the world of rock ‘n’ roll didn’t embrace classical music. I had a great enthusiasm and passion for both.

“As a composer and arranger, I started creating projects like that.”

The show’s origins came about after Fleischer invited singer / actor Rob Evan (Trans-Siberian Orchestra, Broadway’s “Jekyll & Hyde”) to perform during the world premiere of his 2011 classical-meets-classic rock work, “Rock Fusion.” At the time Evan was developing a show called “Rock Tenor.” The two combined their musical visions into “Rocktopia.”

It debuted on Sept. 15, 2012, as the opening concert for the Youngstown Symphony Orchestra season.

Since then, “Rocktopia” has played around the world, including tours across North America, a 2016 performance in Budapest, Hungary that was filmed for a PBS special and a limited-engagement run on Broadway earlier this year that featured special guests Pat Monahan of Train, Robin Zander of Cheap Trick and Dee Snider of Twisted Sister.

On the current dates, “Rocktopia” will have vocalists Snider, Tony Award nominee and “American Idol” finalist Constantine Maroulis (“Rock of Ages,” “Jekyll & Hyde”), Metropolitan Opera tenor James Valenti (“Madame Butterfly,” “Romeo and Juliet”) and We McDonald (2016 finalist on “The Voice”) as well as a five-piece rock band, 30-person choir and 20-piece orchestra.

Besides a change in who sings in “Rocktopia,” Fleischer addressed other changes to the version local audiences attended. “We’ve added several new sequences. We revised some of the sequences that were in the original performance. If you saw the show in 2012, you’re going to recognize parts of it but a lot of it is quite different.”

With a very busy schedule that includes his position as music director and conductor for orchestras in Youngstown; Anchorage, Alaska; and Pougkeepsie, N.Y. Fleischer somehow found the time to be a part of this fall’s “Rocktopia” concerts. The interview for this story took place as he was stuck in New York City traffic prior to the opening night show in Englewood, N.J.

Following the concert in Cleveland, which wraps up the tour, he returns to the podium with the Youngstown Symphony Orchestra on Nov. 3. The program, “In Selfless Service,” honors the men and women of America’s Armed Forces prior to Veterans Day on Nov. 11. It includes selections written by Beethoven, Aaron Copeland, Samuel Barber and Chris Brubeck.