But it was the Impressionists who really opened up a new world of colour and tourism.

In 1874, Claude Monet exhibited a painting of his hometown port of Le Havre called Impression: Sunrise. Was it that revolutionary? After all, the English artist JMW Turner has captured seascapes and sunrises that were even more dreamlike, with borders between light, colour, water and air that were even more permeable. But Monet and the Impressionists had a mission. First, they would get out of the studio and paint en plein air. Second, they’d avoid those grandiose scenes of mountains, Arcadia and battlefields. They’d paint riversides, meadows, chairs, bars, people having lunch and walking through gardens (sometimes with clothes on, sometimes not): and they’d make every scene luminescent, full of colour and lustre.

The immediate beneficiary – and it’s still benefitting to this day – is the French region of Provence. In the same year that Monet showed Impression: Sunrise, the railway opened between Paris and Marseilles. Off south went the artists with their easels, absinthe and mistresses: and we’ve been following them ever since, in search of Van Gogh’s sunflower fields, Renoir’s farmhouses, Raoul Dufy’s balconies – and above all, that shimmering, seductive light and colour.

‘Impression’, painting the psychological effect a scene has on you – a sometimes unbearable effect in Van Gogh’s case – rather than what’s strictly there, was a riposte to the spread of photography. Yet for decades and decades, photography was more interested in news and portraits than landscape; and pretty much stumped by colour. The greatest landscape photographer of all time, Ansel Adams, said shooting on colour film was like playing an out-of-tune piano.