The crowds seemed giddy, almost joyous, wandering from place to place with squeals of glee, greeting strangers with cries of ``Isn't this marvelous!'' Had the Red Sox just won the World Series?

No such luck. It was the opening of a new supermarket.

Last Saturday, Shaw's Supermarkets officially unveiled what it bills as its ``flagship'' store.

Located on Huntington Avenue in the shadow of the Prudential Tower, it certainly doesn't feel like an ordinary grocery store. One enters through a giant glass atrium. Ceilings are unusually high and windows look out to the street. Occupying prime real estate, it may well be the costliest supermarket ever built.

But that's OK. The communities the new store serves - the South End, Back Bay, the Fenway and Beacon Hill - are among the state's most affluent. That's why, even with validation, parking costs $7 just to pick up a gallon of milk.

The 200,000 who live or work in the area are mostly single or couples without kids. They are largely professional, trendy and constantly in a hurry. They eat on the run or, when they serve food at home, buy it already prepared or preseasoned.

They are the kind of people who like to eat, and eat well but don't particularly like to cook.

And so the hallmark of the new Shaw's is not its green grocer (which is really quite small) or its butcher shop (it doesn't have one) but its sushi bar, staffed by three chefs. A carving station at one end of the store slices meats for freshly prepared sandwiches. The cheese shop stocks 150 varieties for easy and exotic snacking.

Those who thronged the store were delighted. But the reasons for their delight were deeper than the presence of an olive bar: In important and unique ways, supermarkets matter.

Parks, town greens or high schools were once the centers of our communities. Today, it's the grocery store. There is no other public place one visits more frequently. It's a spot for news and gossip. It's a place to see old friends, to run into those we've forgotten, or, for the on-the-prowl, an opportunity to meet new ones.

Supermarkets, in short, have become our new common ground.

And because what we eat and how we eat is so deeply part of our cultures, grocery stores also end up being a remarkable reflection of the communities in which they sit. If you want to understand a neighborhood, there is no better place to go than its food store.

During the 1970s and the 1980s, the major grocery chains largely abandoned cities like Boston. Lured by cheap real estate and a burgeoning middle class, they headed for the suburbs. The number of city stores actually declined. Moreover, those that remained were usually smaller, dirtier, poorly managed and more expensive than their suburban brethren.

Boston Mayor Thomas Menino often notes that strong neighborhoods have decent supermarkets; decaying ones do not. Large, well-priced and well-run stores would hold neighborhoods together, he figured. They might, in fact, help to revive those that had fallen on hard times.

His solution: Open new supermarkets.

The Boston Redevelopment Authority adopted that approach, making new grocery stores a key part of its economic development strategy. The results have been striking. The new Shaw's is the 21st supermarket to have opened in Boston the last 10 years. That brings the total number of grocery stores in the city to 35, with another four still in the works.

The first of those, in 1993, was a Stop and Shop in South Bay. Still the largest of the city's grocery stores, it serves wildly diverse Dorchester. An Asian grocery chain, Super 88, that started in Chinatown is now in Allston, and Dorchester. Its presence in those communities also speaks volumes about where the city's new Asian immigrants are settling. Meanwhile leaders in Roxbury are hailing a Stop and Shop that opened in Grove Hall in 2001. It is the cornerstone of a long effort to bring economic revival to a blighted community.

One might question the causality here: Does a grocery store make a community better, or is it an improving community that attracts a grocery store?

Probably it's a bit of both. Shaw's president, Paul Gannon, says falling crime rates were a critical element that revived the interest of large chains in urban areas. Yet in almost every case, the new grocery stores in Boston have had a profound effect on the fortunes of their communities - they not only generate jobs themselves but also, according to the BRA, stabilize a neighborhood and become a catalyst for new economic growth.

It all amounts to an important lesson on good governance. In the broad scheme of things, celebrating a new supermarket might seem a silly thing.

In truth, it's what reviving a city is all about.

Tom Keane can be reached at tomkeane@tomkeane.com.