A tiny figure stands on a strip of pale sand. In front of him is a dark, almost black sea. Above is an immense, empty sky. That is all.

When Caspar David Friedrich exhibited it in Berlin in 1810, viewers were stunned. Paintings were supposed to have a subject, a focus, something to look at. This had almost nothing. One writer said looking at it felt as if your eyelids had been cut off.

Scientific examination has shown that Friedrich originally painted boats on the sea and later removed them, making the scene even emptier and lonelier.

It was bought by the Prussian royal family, who were apparently persuaded by the young crown prince. Two centuries later, it looks strikingly modern — almost like abstract art.