So long, Thanksgiving. You were a special day for more than 400 years, but now it’s all over. Now Thanksgiving is mere prelude to the real celebration. We might as well rename it Black Thursday.

Macy’s, a source revealed to WWD last week, is reversing its traditional policy of staying closed on Thanksgiving after noticing with dismay that much of the crowd that gathered for the Macy’s Thanksgiving Day Parade last year concluded the day by going on a collective shopping spree at rival department store Lord & Taylor, which opened its doors at 10 a.m. as an experiment and drank Macy’s milkshake.

The old-school department stores were the last holdouts. Now L&T, Macy’s, Walmart, Gap, Toys “R” Us and Kmart are all opening Thanksgiving night (and in some cases, even Thanksgiving morning).

Even if such stores hold off opening until 8 p.m., shoppers eager to join the grim rugby match of flattening your fellow citizens in pursuit of one of those $8 toaster ovens or $79 flatscreens will start lining up — when? Six p.m.? Four? Hell, why not noon?

In which case, we might as well rethink the sacred traditional holiday family gathering. How about we all just down a quick Egg McMuffin in the car on the way to the stores?

Thanksgiving has always been a uniquely great American holiday, secular or reverent as you wish, a day set aside for family and gratitude.

Because it has never been linked to exchanging gifts, it has remained free of commercialism. We treat it with the seriousness it deserves. As a people we travel great distances for Thanksgiving, often at the cost of the enormous stress wrought by congestion, because we know how important it is to show family members we love them.

Shopping for gifts for others can be a way of showing love too, and the more money you save on sales, the more gifts you can buy. And today’s Thanksgiving does have some capitalist DNA: At the urging of the founder of the company that today is known as Macy’s, in 1939 President Franklin Roosevelt moved the holiday up from the traditional final Thursday of the month to the fourth one to create a longer holiday shopping season — goosing the economy with an earlier Turkey Day.

But couldn’t the national shopping orgy wait until the day after the holiday, that hideously named Black Friday? Shouldn’t we continue to keep this one Thursday (plus Christmas, the day set aside for consumption hangover) more about the heart than the shopping cart?

Even if every other holiday has turned into an excuse for buying — given how Presidents’ Day has turned out, today’s schoolchildren can be forgiven for thinking it’s an occasion to honor the presidents of Target and Best Buy — Thanksgiving itself was supposed to be fenced off.

It’s reassuring to spend an entire day in the same house with family members we may know well but hardly ever see. We’re supposed to be in this moment together, rolling our eyes at Uncle Earl’s strangely inappropriate jokes and marveling at Grandpa’s foot odors.

No outside force should break that family spell.

After all, it was an underappreciated Founding Father, Jacob Turnbull Winthrop, who wisely decreed that, “Insofar as this Day of Thanks, Rest and Reflection shall be uninterrupted by close Attention being given to vigorously contested Games of Sport, it is hereby ordained that any Matches of Foot-Ball taking place on this Day must involve the Lyons of Detroit.’’

An American immigrant, Christopher Hitchens, pointed out that the very modesty of the day was disarming and attractive.

Hitchens didn’t like turkey (who does?), which became the day’s bird of choice because it was plentiful and relatively cheap. It’s one step up from pigeon.

“Nobody acts as if caviar and venison are about to be served,” the late essayist wrote in 2005.

“The whole point is that one forces down, at an odd hour of the afternoon, the sort of food that even the least discriminating diner in a restaurant would never order by choice.”

Oaken hunks of dark meat, boiled root vegetables and cranberry jelly made from the most bitter imaginable fruit — if these things don’t teach you humility, nothing will.

The search for bigger and shinier objects at the megastores couldn’t be more removed from the Thanksgiving spirit of being content with what you’ve got.

Pausing in the early fall of one of the worst and bloodiest years in American history, Abraham Lincoln made what had previously been a regional tradition into a national holiday.

His proclamation was one of the look-on-the-bright-side statements of history: “Harmony,” he noted, in a statement filled with gratitude for the blessings of American life, “has prevailed everywhere except in the theatre of military conflict.”

Now we trade away whatever domestic harmony we have for a ticket to the theatre of the absurd: Scrambling for position to get a hot deal on a turtleneck at Chico’s.