As the Inquirer's architecture critic, I often receive e-mails seeking information about this or that structure. No building has prompted more inquiries over the years than a mysterious Market Street relic that resembles a cresting ocean wave.

For many years, I also wondered what the peculiar, blank-faced behemoth at 1020 Market St. was used for. Because it has no windows, I thought it might have started life as a movie theater. It wasn't until 2013, when the building made the Preservation Alliance's endangered properties list, that I discovered its impressive pedigree.

Thanks to the Alliance's Ben Leech, we now know that an older building at that address was taken over by Robinson department store in 1946. The new store was designed by Victor Gruen, a prominent Viennese architect who fled the Nazis in 1938 and ended up becoming the father of the American shopping mall. Before Gruen (originally, Grunbaum) rocketed to fame for the Northland Mall outside Detroit, he toiled away in traditional downtowns, giving modernist face-lifts to dowdy commercial buildings. Gruen designed 11 locations for what became the Grayson-Robinson chain. His Philadelphia building is said to be the last one standing.

To appreciate the ambition of Gruen's stylish composition, you'll need to suspend judgment about its condition. That blank facade, which unfurls like a giant scroll, was intended as a cinematic backdrop for the looping Robinson logo, writ nearly two-stories high in neon letters. While metal pins are all that survive of the main sign, you can still see "Robinson" spelled out vertically on the west wall. The cresting wave of the roof served as a kind of modernist eave.

In one sense, Gruen was treating the facade as a simple billboard. But he was also toying with our perceptions of weight. Although the facade is covered in tiny bathroom tiles, flecked with color to add sparkle, the material appears from afar to be polished stone.

In the original design, that elephantine wall perched on three impossibly dainty glass vitrines, suggesting that it was about to crush them. The contrast is what gave the design its dramatic tension. Those displays were filled in long ago for individual shops, including the evocative Funk-O-Mart.

Gruen created Robinson's just as Market Street was entering its final days as a high-end retail hub. Now that the street is on the cusp of a comeback, let's hope someone comes up with an equally clever way to reuse Gruen's sophisticated design.