For some of that time, John Smith, 35, was working on his dissertation for a doctorate in economics. Then, three years ago, Rutgers University in Camden offered him an associate professor's position, and Sevilla Smith, also 35, became pregnant with their son, Max.

The couple needed a permanent address.

While cruising the Web on location in Pittsburgh, Sevilla Smith saw a house for sale - in Elfreth's Alley. She flew in to Philadelphia and bid on it while the open house was in progress.

Talk about steady and secure: The Smiths' peripatetic lifestyle ended on what's considered the oldest inhabited street in the United States, in a National Historic Landmark District.

"When we found this house, it was so great. It was so stable. Kids were playing in the street," says Sevilla Smith, who no longer works full time in the film industry.

For those unfamiliar with Elfreth's Alley, a description:

First, imagine yourself back in time, about 300 years. You are a craftsman or an artisan (a smithy or a carpenter), and you need modest but established lodgings.

North of Market Street and off Second Street, a major thoroughfare in the city, you find what you're looking for - small homes, all connected, but not identical, made of sturdy brick.

To natives of Los Angeles like the Smiths, Sevilla Smith says, old is a house built in the 1920s.

"When we learned about the history of the home, we felt a huge amount of responsibility for making sure the house stays alive," she says. "By that, I mean, we didn't feel as though we wanted to take it back to colonial times, but to make it very much not only a part of history, but part of today."

And it is. Many of the house's original features are still there, like the huge fireplace in the living room, which the family uses a lot, Sevilla Smith says. Also still intact are the floors, the cupboards, the doors - all made by early Americans. The couple installed bolts under the slanting floors to support them.

This particular house has three stories. The front part, built in 1757, once sheltered three families, who shared the basement for cooking.

In 1800, the dining room was added, as well as the kitchen behind it.

Today, it's a very modern kitchen, with black granite countertops, loads of maple cabinets, and a pale-green fiberglass backsplash. The floor, which Sevilla Smith says she installed, is made of two-foot-square pieces of birch and oak.

"When I saw the kitchen, I said, 'This is perfect,' " says Sevilla Smith, who owns an eponymous clothing store in Old City.

What strikes a visitor, though, is how stark, yet rich-looking, the house is. Just as every home is an amalgam of the lives of its occupants - their histories, their lifestyles, their culture, their tastes - so, too, is this home.

Sevilla Smith, who lived in the Philippines as a child, likes clean-looking surroundings. There are no fabrics on the floors. "I don't like rugs . . . rugs feel very dirty," she says.

The palette of choice is white. White walls, white curtains, even a white sofa - a brave choice with a 2-year-old. Even the bathrooms are white and black (there's a black granite shower).

Set against against this whiteness is furniture made from deep-colored woods.

Sevilla Smith spent time shopping while on film locations. In Morocco, she bought a teak side table with a camel-bone inlay. In the couple's bedroom is a king chair with mother-of-pearl inlay. In the living room is an armoire from China that she found in an Los Angeles antiques shop.

What's also striking is the juxtaposition of 1750s artistry and 2010 technology.

After ascending a winding staircase, a visitor reaches the attic; it's here that John does his research in behavioral economics. And you'll find what's to be expected these days: computer; printer; scanner; and other high-tech gadgetry.

Only a few feet away are the attic's original windows, which open out to the roof. The family climbs out there to watch fireworks displays over the Delaware River, Sevilla Smith says.

The attic itself has been painted white. "It felt dark and confined," she says. "Now, it doesn't feel so much like an attic."

The house is devoid of tchotchkes, but what must be mentioned is John's vinyl collection. His face lights up when it's noticed.

Occupying a case that's at least five feet high, the collection, primarily punk-rock artists, was constantly in use when he was a DJ at WPRB-FM (103.3) in Princeton, where he studied for his doctorate.

"I had a weekly three-hour show," he says.

Living on a historic street is a constant show. Sevilla Smith says you never know what language you'll hear from the tourists who pass by.

But the hubbub doesn't bother them. "Once you shut the door," she says, "you shut the city off."