As we drove along these long beautiful stretches, it occurred to me to ask, Who was responsible for the planting of these magnificent trees and (therefore) when was it done?

Many answers were vague; Napoleon, I was told. But which Napoleon? And why? To give shade to troops (or farmers), I was told. This would mean that the trees are 150-200 years old.

Is this myth or truth? Does anyone know?

BTW, they are unforgiving when met by an errant car; I was told Camus met his fate this way...

I don't know either but I understand that many French Mayors want them taken down as they often leap in front of drivers after a long lunch and present senior, up right citizens in the light as "drunken fools".

I too would like to know the answer to your question

Horticulturally speaking, it's usually a mistake to plant en masse one species. If disease strikes one tree, it can contaminate all of them, as it has along one road in L'Isle sur la Sorge.

We were told that they were planted by the King in Paris (Louis the whatever?) in order to shade the routes from the country into the city, such that produce, meats and seafood could be brought in with less chance of spoilage.

Two years ago, in early spring, we watched them being pollarded by the most incredible piece of heavy equipment. Had always wondered how they kept after them.

Searching the French web, I found that the most common answer was that Bonaparte had the trees planted to shade military movements.

It is true that the trees are now considered to be killers and hundreds of thousands of them have been removed. Also, in a lot of places, there is only one row of trees as the other row was removed to widen the road.

New trees are being planted along roads, but nearly always completely out of reach of the possible trajectory of cars. I am among those who lost a cousin, age 20 (and a non drinker), to a plane tree along a country road. The survivor from the car said he was trying to avoid a fox.

Bringing this to the top again for those who might have missed it...

(Now that Stu D is back, perhaps he'll chip in with a definitive answer.)

The Bonaparte theary is what I have read in the past. Some of thes allées have died s result of a parasite fungus canker.