Ground was broken on the arena on June 1, 1966, by Jerry Wolman and then-Philadelphia Mayor James Tate as the home of the NHL's expansion Philadelphia Flyers. The first event at the arena was the Quaker City Jazz Festival on September 30, 1967, produced by Larry Magid. The first sporting event at the arena was an October 17, 1967 boxing match featuring Joe Frazier vs. Tony Doyle. From 1967 through 1972, fifteen fight cards were held at the Spectrum. The NBA's 76ers also moved there from Convention Hall as a second major league sports tenant. Lou Scheinfeld, former President of the Spectrum, explained that the name "Spectrum" was selected to evoke the broad range of events to be held there. "The 'SP' for 'sports' and 'South Philadelphia,' 'E' for 'entertainment,' 'C' for 'circuses,' 'T' for 'theatricals,' 'R' for 'recreation,' and 'UM' as 'um, what a nice building!" Scheinfeld also said that a seat in the city's first superbox initially cost $1,000 a year: "For every Flyers game, Sixers game, circus, you name it, you got 250 events for $1,000." The Flyers won their first ever home game in this arena by defeating the Pittsburgh Penguins, 1–0. Bill Sutherland scored the arena's first goal.
On March 1, 1968, wind blew part of the covering off the Spectrum's roof during a performance of the Ice Capades, forcing the building to close for a month while Mayor Tate fought with then-Philadelphia County District Attorney Arlen Specter over responsibility for the construction of the roof, and the damage was repaired. The 76ers moved their home games to Convention Hall and to the Palestra, but neither of those arenas had ice rinks at the time, and there were no other NHL-quality sites in the Philadelphia area. Thus the Flyers hurriedly moved their next home game (against the Oakland Seals) to Madison Square Garden in New York followed by a meeting with the Boston Bruins played at Maple Leaf Gardens in Toronto before establishing a base at Le Colisée in Quebec City, home of their top minor league team, the AHL Quebec Aces, for the remainder of their regular season, marking the first NHL games in Quebec City in over four decades, and years before the Quebec Nordiques joined the NHL. (The roof was repaired in time to permit the Flyers to return to the Spectrum to open their first Stanley Cup playoffs against the St. Louis Blues on April 4, 1968; the opening faceoff came just as the assassination of Martin Luther King Jr. was transpiring in Memphis, Tennessee.) Similarly, in 1993, the Flyers played a day game against the Los Angeles Kings during a blizzard. A piece of flying debris smashed out one of the concourse windows, cancelling the game just after the first period.
In the 1970s, the venue's location on Broad Street and the reputation for fisticuffs that the Flyers had developed led to the nickname "Broad Street Bullies."
A plaque inside The Spectrum stated that it held the world record for the fastest conversion from Hockey to Basketball.