On this day in history, June 1, 1967, the Beatles released "Sgt. Pepper's Lonely Hearts Club Band," their 8th album — which became the soundtrack to the "Summer of Love," according to the official website of the Beatles. 

With its 13 songs, the album was recorded in over 400 hours during a 129-day period, according to The Beatles Story, Liverpool, a museum in Liverpool, England, that shares the history of the band. 

On a return flight to London in November 1966, Paul McCartney thought of the idea for this album, the same site indicated. 

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"Unable to sleep, he toyed with the idea of creating a new identity for the band, to allow them to experiment, with each Beatle taking on an alter-ego in the ‘Lonely Hearts Club Band,'" the same source says. 

"During the flight, a conversation about the ‘S’ and ‘P’ markings on the salt and pepper sachets occurred between Paul and Mal Evans, the Beatles’ road manager, and sparked the idea for the title ‘Sgt. Pepper.’"

Work had begun on the album in late 1966, and at one point in time, it was thought that both "Penny Lane" and "Strawberry Fields Forever" would also be included — but each of those songs was released as a single in February, so that idea was abandoned, says the Beatles' official website.

The "Sgt. Pepper's Lonely Hearts Club Band" album, considered by many to be the greatest record of all time, featured such Beatles' classics as the title track, "Sgt. Pepper's Lonely Hearts Club Band," "A Day in the Life," "Lucy in the Sky with Diamonds," "With a Little Help From My Friends" and "When I’m 64." 

The title track, "Sgt. Pepper’s Lonely Hearts Club Band" is a song written by Paul McCartney (credited to Lennon-McCartney), says the Paul McCartney Project. 

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The song appears twice on the album: as the opening track (segueing into "With a Little Help from My Friends") and as "Sgt. Pepper’s Lonely Hearts Club Band (Reprise)," says the same source.

The album has sold over 32 million copies worldwide. It is one of the highest-selling albums of all time, recounts the same source. 

The album spent 15 weeks atop the Billboard album chart and enjoyed 113 consecutive weeks in the Top 200, said the same source.

The music on the album was both exciting and groundbreaking, as was the way the recording was delivered. 

"The glossy double wallet featured the guys in their Pepper uniforms surrounded by images of people they either admired or were interested in, [while] on the back of the sleeve there were the lyrics to all the songs," according to Beatles' official website. 

Also, inside each side of the wallet were other surprises, including a card featuring various cut-outs — and in the initial pressings, at least, the paper inner sleeve bore a psychedelic design, the same site says.

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In 1967, critic Kenneth Tynan of The Times of London called the release of "Sgt. Pepper" "a decisive moment in the history of Western civilization," says History.com. 

"Sgt. Pepper" is often referred to as the first "concept album" — and it's often named as the inspiration for other great musical acts of the 1960s, from the Rolling Stones and the Beach Boys to Stevie Wonder and Marvin Gaye, says History.com

The year 1967 marked not only this creative monumental album release, but the start of a three-year period in which the Beatles recorded and released five original studio albums.

Two of those — 1968’s "The Beatles" (aka "The White Album") and 1969’s "Abbey Road" — occupy the 10th and 14th spots, respectively, on Rolling Stone magazine’s list of the greatest albums of all time, notes History.com.

Also in the top 15 on that list are "Rubber Soul" (1965) at #5; "Revolver" (1966) at #3; and "Sgt. Pepper’s Lonely Hearts Club Band: at #1, History.com indicates. 

The "Sgt. Pepper" album was inducted into the Grammy Hall of Fame in 1993.

In 2003, it was chosen by the Library of Congress to be added to the National Recording Registry, noted ABC Audio Digital Syndication.

The album’s accolades, when added to the National Recording Registry, "highlighted the creativity and timeless ingenuity of the Beatles’ talents: 'Sgt. Pepper’s Lonely Hearts Club Band' remains perhaps the quintessence of rock ‘n’ roll artistry," said author Bob Spitz for the Library of Congress. 

Spitz wrote a definitive biography of the band, "The Beatles," which was a New York Times bestseller.

The album marked a cultural and artistic watershed for the Beatles in 1967, according to the same source.

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"A breakthrough album deserved a cover worthy of the music, and the Beatles delivered a doozy. ‘Sgt. Pepper’s’ demanded a bold departure: not merely a cardboard slipcase, but something fresh, entertaining, experimental — radical," notes the same source.

The Oxford Encyclopedia of British Literature called the album "the most important and influential rock ‘n’ roll album ever recorded," says Guitar International Magazine.