In some ways, it was a well-planned fete.

A concept years in the making. Guest list resolved. Date and time chosen months ahead. Place identified.

Champ de Mars, in the shadow of the Eiffel Tower. Near the dirt allee named Thomy-Thierry.

The trouble with that?

The Champ de Mars is a very big place. And acres of it abut the dirt lane named “Thomy-Thierry”.

When we arrived, we joined a crowd of oh, perhaps, 100,000 sun-kissed tourists wandering through the champs or under (or in) the Eiffel Tower, which is near the northwest end of the field.

I have been in or around the Champ de Mars dozens of times … and I cannot remember seeing more people in the area — aside from when the Three Tenors performed, the night before the 1998 World Cup final.

It was a United Nations of tourists.

So, we were going to meet up with about 25 people, some of whom we had not seen in a decade, from among tens of thousands of strangers, somewhere in the middle of this X-square-mile park.

What could go wrong?

Without access to the internet, without phone numbers for more than a handful of the invited and without so much as a flag or banner to plant in the ground or wave in the air.

We found a “trianglular” area (a code work sent out in the invitation) next to Thomy-Thierry … but realized the dirt path ran on for another half a mile.

We separated. One to hold the spot, two to sit and scrutinize passersby (few of which they would recognize) and a fourth to stare at everyone (especially those looking lost) while walking slowly southeast.

The Miracle of the Champs was running into the first two people, and recognizing them and remembering their names, and taking them back to the camp.

The turning point came 15 minutes later — when one of those arriving for the fete texted to one of us: “You are in the wrong place. Find the red-and-pink balloons.”

Someone not even in France had the foresight to have one of the guests bring a bouquet of large, helium-filled balloons and, suddenly, winnowing out friends from the enormous crowd became much easier.

Within a few minutes, the Champagne corks were popping amid lots of hugs and bisous. It became the Eiffel Tower Miracle Party.

A milestone birthday was celebrated one more time, with memorable scenery and lots of newspaper stories, some of them even true, others embellished only for the purposes of improving the anecdote.

“So, the shrimp story …”

“And then she said: ‘Pardon my French!'”

We stayed until dark, and took full advantage of French law — which does not prohibit drinking in public places — and had a fine time till the evening came, along the first drops of a storm.