The roof of the arena is supposed to start collapsing this afternoon, after support beams are removed, according to Comcast-Spectacor spokesman Ike Richman.

Expect the tumbling to begin around 2 p.m. - a two-hour delay from an earlier estimate, Richman said.

Anyone who wants to see a wrecking ball begin to crush Philadelphia's beloved Spectrum should be in the parking lots adjacent to the South Philadelphia arena by mid-day Tuesday.

In a ceremony that is hailed as a "block party," complete with dollar hot dogs and sodas, the exterior walls of the arena that hosted thousands of Sixers and Flyers games and hundreds of rock and pop music concerts over the last 42 years will face a wrecking ball at noon, officials said.

Sports icons, Julius Erving of the Sixers and Bobby Clarke and Bernie Parent will be on hand and speeches will be delivered by Mayor Nutter, Comcast-Spectacor chairman Ed Snyder and others, officials said.

During the festivities, fans can place orders for commemorative bricks from the arena for $39.95, Richman said.

The parking lots around the Spectrum will open at 9 a.m. The demolition is expected to take about four months, Richman said. The Spectrum is to be replaced by Philly Live, a retail, restaurant and entertainment venue that is expected to be completed in 2012.