Archibald Query of Somerville came up with the recipe for Marshmallow Fluff 95 years ago, selling it door to door until World War I created sugar shortages and he sold out to a candy company. That was before his recipe became a favorite of sweet-toothed kids around the world, looking for a way to counter the heavy taste of peanut butter. Query’s invention didn’t make him rich and didn’t make kids any healthier. But it did create some indelible childhood memories. And today, it provides a pretext for a union that once seemed even less likely than peanut butter and Fluff: that of the proudly working class “old Somerville” and its artsy cousin, “new Somerville.”

Not too long ago, old Somerville, based largely in the eastern side of the city, both feared and disdained the many Cambridge types moving over the border to neighborhoods like Davis Square, in western Somerville. The encroachment started in the 1970s, during a brief and unfortunate time when Cantabrigians had a fondness for denim overalls and peasant skirts — hence the nickname they received from their chortling neighbors in old Somerville: “Barneys,” like fake farmers in their barnwear. The term still arises in various Somerville chat rooms and blogs, but with less rancor than before. Both old and new Somerville are doing well, buoyed by improving transportation, property values, and job creation.

That provides some of the neighborhood background for the seventh annual Fluff Festival, scheduled for Saturday in the aptly named Union Square. The square was once an enlistment spot for Civil War troops, but more recently has been a dividing line between east and west Somerville. Now, with both battles over, people from throughout the city and beyond will come together to eat fluff, learn about shared history, and listen to live music. This increasingly popular event, combining the best of the old-fashioned town fair and collegiate arts festival, honors more than just Archibald Query and food that sticks to your face. It celebrates civic virtue in all its forms, along with the principle of neighborhood pride.