This movie was filmed entirely on location in Provence, France.
First....Lonsdale is NOT dubbed. He is of both French and English parentage and completely at home inboth languages. In Europe, a "Caravan" is what Americans call a Trailer.
This movie was made and released about four years after its source novel of the same name by Alistair MacLean was first published in 1970. 'Caravan to Vaccarès' was MacLean's fifteenth novel and this movie was the ninth film adaptation of one of MacLean's stories.
The full name of the Duc de Croyter character played by Michael Lonsdale is Le Grand Duc Charles de Croytor. His nickname is "The Duc".