It's been less than 30 years since One Liberty Place overtook William Penn's statue atop City Hall as the highest point above Philadelphia. Our city has seen its fair share of high-rise development since the mid-1980s, but imagine how it would look if zoning issues, financing woes, and a sputtering economy were never factors in the skyline's evolution.

Sure, the newly approved FMC Tower in University City and the rumors of a Norman Foster supertall to accompany the Comcast Center are exciting, but their potential impact on the skyline doesn't come close to these 15 failed proposals, many of which were killed off when the housing bubble burst in 2008.

There are certainly a few honorable mentions, like the originally-planned twin to accompany the G. Fred DiBona Jr. Building (IBX Tower), the super-ambitious Philadelphia River City, and 205 Race Street, but feel free to sound off with your own suggestions in the comments.