Why does Old City keep burning?

The blocks between the Delaware waterfront and Independence Mall are home to one of the richest collections of architecture in all of Philadelphia, with buildings that track the nation's evolution from colonial settlement to industrial powerhouse. Now an upscale neighborhood of loft-style apartments, Old City hardly lacks for activity; its streets are thick with fine restaurants, vintage furniture stores, and clothing boutiques that lure locals and tourists alike. The neighborhood has become a magnet for creative businesses and tech start-ups. And yet, in the 15 years since the city declared the area a historic district, Old City has lost no less than five distinctive, 19th-century commercial buildings to fire and other unfortunate events.

Friedman's Umbrella went up in flames 2004. The Five Spot succumbed in 2007. The Shirt Corner and the Suit Corner were lost within a few weeks of each other in 2014, one to fire, the other to structural issues.

But the latest blaze, which swept through a trio of mid-19th century merchant buildings over the quiet holiday weekend, is the most devastating loss yet. Those five-story lofts virtually define the look of Old City. Designed to mimic Italy's Renaissance palaces, they are part of a stunning ensemble that stretches virtually uninterrupted along Chestnut Street from Second to Fifth Streets. At least one of the three buildings is said to be a goner. A second will require heroic efforts to repair.

It's not too much to say that this string of Chestnut Street buildings is the reason Philadelphia exists. Born as a trading city, Philadelphia grew from its port on the Delaware and then migrated up Chestnut and Market Streets. First came suppliers and shippers, warehouses and small manufacturing buildings, on the 200 block of Chestnut. They were followed on the 300 and 400 blocks by the stately banks that financed their activities.

The flames did their worst damage to 239 Chestnut, where the blaze began. But at least two floors of 237 were charred, and 241 sustained water damage.

The building at 237 is a particularly notable part of Philadelphia's history. Emblazoned with the name "Leland" on its massive granite cornice, it was designed in 1856 by Stephen Decatur Button and probably served as the headquarters for a wine and spirits manufacturer. It is such an elegant piece of work that when the famous Chicago skyscraper architect Louis Sullivan arrived in  Philadelphia in 1873 to apprentice under Frank Furness, he singled out the design as a source of inspiration.

It's true that old buildings like these are prone to fires. Although we admire Old City's multi-story loft buildings for their imposing stone and cast-iron facades, their innards are made of weaker stuff. Erected before buildings rose on steel frames, they were constructed with thick timbers hewed from America's virgin forests. And while those muscled, 4-by-10 beams may make today's 2-by-4s look puny, they are no match for flames ignited by faulty electrical systems, old rags, or machine oil embedded in their wood floors.

While it will take some time for city fire marshals to determine the cause of Sunday's fire, that doesn't mean that the blaze, and the ones before it, couldn't have been prevented.

Despite being a desirable neighborhood, Old City is not always a well-kept one.

"Old City has a surprising number of blighted, poorly maintained buildings," said Paul Steinke, head of the Preservation Alliance for Greater Philadelphia. You only have to stroll along Second or Third Streets to see buildings with stone peeling off the facades or wood that hasn't been painted in decades.

Yet even those that have been well-kept tend to lack a crucial form of fire protection: sprinklers.

After the 38-story One Meridian Plaza across from City Hall was destroyed in a 1991 fire, sprinklers became mandatory in high-rise commercial buildings — but not in smaller structures like those in Old City. While a few owners have voluntarily retrofitted their buildings, most have not been willing to invest in fire suppression systems.

The building at 239 Chestnut was one of those buildings without sprinklers, David Perri, commissioner of the Department of Licenses and Inspections, told me. Unlike its neighbors, its facade was primarily wood, coated with stucco. Only the ground floor was cast-iron, and that is the only part likely to survive.

Perri said it would have probably cost no more than $75,000 to equip the building with sprinklers. Now that federal tax programs allow owners to write off the investment, the out-of-pocket cost is much less. Putting in sprinklers would  also reduce the cost of the owner's building insurance premiums.

So why don't more Old City landlords make the investment that could protect their property?

Unlike other parts of Center City, Old City is still dominated by small, single-building landlords rather than large property owners. Many have owned the buildings for decades. They've gotten by without doing much to improve their properties.

Thankfully, no one was killed in this latest Old City fire. But as architectural casualties pile up, we are losing more of our city's irreplaceable patrimony.