NEW YORK CITY – Friday night in the big city, I’m bopping along Fifth Avenue with my brother, and the place is one huge construction site. But this evening’s industriousness differs from the usual after-hours midtown work. Guys aren’t pouring new cement, climbing out of sewer manholes or replacing air-conditioning systems. They’re not unloading truckloads of girders or elevator parts.

They are basically building the stage for the annual New York City Christmas show.

Vans piled high with identically cut evergreen branches idle in front of Tiffany’s.

Across the street, a truck the length of a commuter jet double-parks with its load of 8-foot-high snowflake cutouts.

Near Radio City Music Hall, electricians crawl over a fanciful display of Christmas tree lights, each the size of a third-grader.

This is the material experience of Christmas in the city. Creating this fantasy is not a job for a skinny geek with some cool software. There’s nothing virtual going on here. This is touch-see-smell toil, and the laborers are (mostly) men with muscled backs, greasy hands and mechanical skills.

Fabulous holiday extravaganzas are coming together in downtowns across America, but will they amply reward city treasuries and the retailers who pay real estate taxes?

One hopes so, but the forces of e-commerce continue their silent march on the consumer purse.

Even big-box discounters must take note: Their “black Friday” retail blowouts are being challenged by online specials that start on Thanksgiving Thursday itself.

This year, shoppers camped out overnight for the Walmart “door-buster” bargains need not inconvenience themselves (if they’re doing it for the deals rather than the spectacle).

Best Buy, Macy’s, JCPenney and other brick-and-mortar merchants are now joining Walmart in offering significant discounts online – and they’re not waiting until Friday.

Retailers used to back off from Thanksgiving, a spiritual holiday with limited merchandizing opportunities. People generally don’t send Thanksgiving cards or buy Thanksgiving presents.

Once you own the turkey salt and pepper shakers, there’s no need for an upgrade.

Some stores shocked Thanksgiving purists a few years ago when they opened for business on that Thursday. Many are now starting virtual door-buster sales on the national day for giving thanks.

They say that’s what the public wants, and they’re probably right.

Some online activities may make one element of the physical holiday season more pleasant. Muggings increase this time of year. This is hard to believe, but many criminals like to brag about their deeds on Facebook, YouTube, MySpace and other social networking sites. That makes the police detective’s job considerably easier.

For example, a thug who robbed a man at a bus stop posted a picture of himself on MySpace holding the victim’s stolen ring. The mugger bragged, “I’ve got new bling!” according to the New York police. His arrest was swift.

Of course, the Internet shopping experience can be its own swamp of cons, identity thieves and fraudsters of all variety.

And try to find a perpetrator out in cyberspace.

Anyhow, back in the world of sweat, biceps and 100-pound ornamental candy canes, the downtown people are going through the trouble.

Surely they must wonder the extent to which their spectacular street lighting, animated window displays and music will bring shoppers to their points of sale.

There’s the concern that folks will play with the beautiful merchandise, then order it online.

But if holiday shopping is to remain a rich tradition, there’s no substitute for joining the cast and participating in the same downtown pageant.

Sure enough, the work crews were gone by Saturday morning, and the sidewalks filled with parents and kids and strollers.

There’s nothing like a live show.