History is Philadelphia's brand. The city is America's birthplace and the nation's only World Heritage City. Yet, the city is gift wrapping many of its most-prized historic, architectural, and cultural gems and topping them with a bow for developers instead of preserving such treasures.

Jewelers Row, for example, is the country's oldest diamond district, home to nearly 1,000 merchants, artisans, and craftspeople. Dating to 1852, the charismatic neighborhood draws shoppers and tourists, and is as uniquely Philadelphian as the Italian Market, Rittenhouse Square, or Boathouse Row.

Such an iconic landmark one block west of Independence Hall certainly should be protected from development - right? Apparently not.

Instead of being protected in a city-designated historic district, the 700 and 800 blocks of Sansom Street are zoned for the tallest, densest, mixed-use development - a bauble beckoning builders. Swooping in is Toll Bros., the Horsham-based builder, which is poised to demolish the core of Jewelers Row to erect a 16-story, 80-condo tower.

Plans call for five street-level shops along 90 feet of frontage. The tower would be set back 15 feet from the sidewalk, but it will stick out like a sore thumb extending above the eclectic mix of four- and five-story brick rowhouses. Worse, it will change the block's identity, function, and economics.

Mayor Kenney pledged to make historic preservation a priority, but he has been disappointingly silent on the threat to such an important district. He has failed to increase the city Historical Commission's budget or establish new historical districts, both of which he urged as a councilman.

The Historical Commission, which should be the city's watchdog and champion for its historic features, also has been strangely MIA since it took a pro-development turn on former Mayor Michael Nutter's watch. A 10-year pass on real-estate taxes has fueled the resurgence of the housing market for millennials and empty-nesters flocking to the city, but such growth should not come at the expense of the history and character that are drawing them.

That's the real, insidious crisis threatening Philadelphia: its disappearing identity.

The Boyd Theater, Society Hill Playhouse, Whitman's Chocolates factory, and dozens of churches have been lost. Stately Victorian townhouses near Drexel University and the University of Pennsylvania are being erased for student housing.

Only about 3 percent of the city's buildings are designated as historic, compared to 28 percent in Manhattan, 19 percent in Washington, and nearly 6 percent in Baltimore.

How can that be?

The threat of losing the heart of Jewelers Row is a wake-up call for the city to embrace and protect its very essence.

The mayor should follow through on his promise - and the recommendations of local preservationists and the state Historic Preservation Office - by ordering a citywide survey of historic buildings. He also should increase staffing and funding for the Historical Commission and re-chart its course. And he should promote the 10-year property-tax abatement for rehabilitation projects.

Philadephia is known worldwide as a historic and eclectic collection of neighborhoods. Its jewels must be protected immediately and aggressively.