She didn't even wobble as she strode - sailed gracefully, actually - across the grass from her old home in the White House to the Naval helicopter waiting to carry her on towards the swards of the Trump golf club in Florida (and to what she might have felt was freedom).

How did she keep her balance, let alone her poise? It's all my high-heeled friends (mostly women) have talked about since.

One who wears heels nearly as high as Melania's concludes that the former first lady must have been on tip-toes - but she wasn't.

Another thinks there must be boards just below the surface of the South Lawn.

Or (and this is the most credible theory) the ground was frozen - except that the temperature only went below freezing in the middle of the night, and the Trumps left in daylight.

The grass looked sodden. And she was wearing sunglasses (which suggests sun). Even the dullest detective in the Capitol Police could tell you this does not suggest frozen solid ground.

Women's Wear Daily, ("the fashion-industry trade journal sometimes called 'the bible of fashion'") observed that Mrs Trump III was wearing "a short black Chanel jacket with gold buttons, a black Dolce & Gabbana dress, black gloves and sky-high stilettos".

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WWD opines: "The all-black ensemble seemed to bookend the pale blue custom Ralph Lauren bolero and dress that she wore for Trump's swearing-in four years ago".

The "sky-high stilettos" do make Mrs Trump seem as tall as Mr Trump, something you might think he'd mind, but there we are. Good on him for his sense of equality.

It's all a great mystery - but not as great a mystery as why women wear heels that high.

Shoes are clearly a statement - think of Julie Bishop with the racy red shoes she wore when she resigned as Australia's foreign minister. They were such a statement that the Museum of Australian Democracy put them on display.

"The shoes she was wearing - red satin with bejewelled heels - stood out in the sea of black and white," The Canberra Times reported at the time.

"When in doubt wear red," Ms Bishop said.

"Red is one of my favourite colours. It evokes power, passion and fashion. It symbolises courage and freedom. Passion, well, you know, red hearts, red roses.

"And fashion - that's why they call it a red carpet - and red lipstick, red nail polish, red shoes."

Melania Trump's shoes were black, so what does that symbolise?

Another fashion bible, Grazia, has a theory: "Melania Trump chose a rather funereal outfit of all-black as she left with her husband.

"A chic outfit, it must be said, as it was made by Chanel. Whether or not the French fashion house is pleased to have been the choice of departure outfit for the least popular first lady in American history remains to be seen."

The obvious conclusion is that Melania was wearing black in mourning for the loss of power - except she has seemed quite chirpy recently.

The tirades and tantrums of their final days in the bunker may have got to her. "Do I really need this?" she may have asked, and who could blame her?

"She just wants to go home," a source told CNN. "Asked how the first lady feels about rumors her husband might announce a 2024 bid, the source added: 'That might not go over well'."

So much mystery. Why didn't the heels sink in?

And the mystery of love: What does Melania see in Donald?

And the biggest mystery of all: what did the American people see in Donald Trump?