6/5/2019: The "Vertical Airstrip"

I NEED YOUR HELP ON THIS ONE:
In a section of my book, “A Spear Carrier in Viet Nam,” entitled “Short Flights on Dubious Airlines,” I describe a visit to Vientiane, Laos (via Royal Air Lao!), largely to see the structure in the photo below. I say “largely,” because by 1972, you couldn’t go outside the capital, and there wasn’t much to see inside it.
The photo, taken by me, is of a substantial (for SE Asia) arch then in “downtown” Vientiane. I have no idea if it is still there. Note that while it was clearly built for vehicular traffic, the only person visible is walking.
Everyone in CORDS knew it as “The Vertical Airstrip.” So did the Lao cyclo drivers who took us there from our hotel; that’s all I had to tell them.
Its conventional-wisdom backstory was that, some time earlier, the U.S. had granted some money to build an airstrip somewhere out in the country to actually prosecute the war, but the Lao, rational and peace-loving people that they are, chose instead to spend the money on this impressive arch.
That was the CW, but anything as substantial as this had to have a more official story. Can anyone help me with this?

People did! It’s still there, and its backstory is still uncertain. It is known as the “Patuxai”.