The French painter Henri Rousseau was a self-taught artist. This meant that without trying he was free from the academic skills laboriously acquired by artists trained in conventional ways of drawing and painting, who drew from the posed model and casts of classical sculpture, and worked in a hand-me-down tradition reaching back to Raphael.
By the end of the 19th century, some adventurous artists were concluding that this tradition had become so tired that modifications to it were no longer enough. It needed to be hit out of the field.
When Rousseau found a way of exhibiting his pictures publicly, many visitors came to scoff and laugh. He was so obviously incompetent, they thought. But there emerged a number of avant-garde artists and writers who started to take seriously the very things about Rousseau that others ridiculed - chiefly his lack of academic skill. This naive - but highly serious - painter seemed to suggest a way of escape from the conventional impasse they believed art found itself in.
Picasso, one of Rousseau's appreciators, bought several of his paintings. The first was a female portrait that cost virtually nothing. The owner of the shop selling it suggested Picasso just paint over it. But Picasso not only considered the painting a psychological masterpiece, he refused ever to part with it.
It was ironic that Rousseau himself had no wish to escape from the accepted conventions of art. He wanted to be shown at the official annual salon exhibition rather than at the independents show where everyone was free to exhibit. He hadn't a hope. The jury would have dismissed him as a clueless amateur. It has proved even more ironical that history has virtually canonized Rousseau as an essential link in the chain of modern art, while the academics of his time have been relegated to an obscurity from which, even today, few have been rescued.
The latest heavyweight recognition and scholarly reassessment - "Henri Rousseau, Jungles in Paris," is currently on view at the Grand Palais in the French capital, the artist's home city. Later this year it will be seen at the National Gallery in Washington. The exhibition started out at London's Tate Modern.
Rousseau's dreamlike visions of jungles vie with his paintings of Paris and its suburbs. Neither are realistic. They are highly imaginative studio re-creations underpinned by selective observation of the real world.
Even "The Customs Post," although it can be associated with a specific site, has been altered into a typical image of Rousseau's own making. And it must have had personal significance, since he had, before becoming a full-time professional artist, worked for the octroi, Paris's toll-collecting service. It was this that earned him his (rather patronizing) nickname "Douanier," or "customs officer."
There have been many "naive" artists - a deluge following Rousseau throughout the 20th century - but few have had the solemn, discreet authenticity and certainty of their own vision that he had. It's a vision made convincing by his lack of training rather than in spite of it.
• 'Henri Rousseau, Jungles in Paris' is at the Grand Palais in Paris until June 19. It will be at the National Gallery in Washington July 16 through Oct. 15.