Hamburger Kunsthalle audio guide,
five stops, free.

He has his back to you, and he is never going to turn round. A man in a dark green coat, standing on a spur of rock with a walking stick in his right hand and the wind in his hair, looking at something you are not allowed to see. Ninety-five centimetres by seventy-five. Smaller than the posters.

Caspar David Friedrich painted it around 1817. The Kunsthalle says about 1817 rather than a firm year, because he never signed it and never dated it, which is also why you will find 1818 printed in plenty of books.

The landscape is real, and it is not one place. Friedrich built it out of drawings made on walking trips in the sandstone country south of Dresden, hundreds of kilometres from here. The rock the man stands on comes from a sheet he drew on the third of June 1813, climbing a hill called the Kaiserkrone, and in the margin of that drawing he wrote himself a note about exactly how high above the highest point of the stone the horizon should sit. The cone-shaped mountain far to the left is the Rosenberg, from a study made in May 1808. The flat-topped block answering it on the right is the Zirkelstein. The jagged formation in the left middle distance is the Gamrig, near Rathen, tidied up a little. He assembled a country that does not exist out of places that do.

So who is he? Nobody knows. The Kunsthalle is blunt about it: there is no reliable evidence by which the man can be identified, and the periodic attempts to name him rest on nothing. What the museum will say is that Friedrich probably did not intend you to climb inside him. You are standing behind a person who is standing in front of a view, and the view is withheld. The subject of this painting is not the mountains. It is somebody looking at mountains, and you looking at him.

It is unusual for Friedrich in two plain ways as well. He rarely painted upright. And he rarely put a single figure this large, this unmissably, in the middle of anything.

The route to this wall was not smooth. As late as 1947 the picture was being exhibited under the wrong name, catalogued as a work by Friedrich's contemporary Carl Gustav Carus and titled Wanderer at the Abyss. In July 1949 a Berlin dealer offered it to the Hamburger Kunsthalle, and the director of the day, Carl Georg Heise, turned it down. It took another twenty-one years. In December 1970 Werner Hofmann, one year into running this museum, talked the Stiftung für die Hamburger Kunstsammlungen into buying it through a Stuttgart dealer for six hundred thousand Deutsche Mark. It has hung here on permanent loan from that foundation ever since, and in the half century since then it has become the most reproduced German painting of the nineteenth century.

A woman with her hands clapped over her face, a blue robe whipped away from her, and a bench of men in red staring. Gérôme has painted the exact second of an unveiling staged inside a court of law, and he has put you in the seats.

The story is Greek and very old. Phryne was a hetaira, a courtesan, from Thespiae, and she is supposed to have modelled for Praxiteles when he carved the Aphrodite of Knidos. She was put on trial for impiety, the charge being that she had compared her own beauty to the goddess's. When the verdict looked like going against her, her defender Hypereides pulled the robe off her, and she was acquitted. The Kunsthalle calls the picture an example of the victory of seeing over speaking.

Look at what she does with her hands. She covers her face, not her body. The museum has a phrase for it, a revealing concealment: she hides in shame and exposes herself in the same movement, and Gérôme knew exactly what that would do to a room.

Then look at the judges. Rows of red, leaning, craning, one of them at the back on his feet with both arms flung up. And in the middle of it, on a pedestal, a small gold figure of Athena with her name written in Greek on the base. The goddess is the whole point of the charge, and not one person in the picture is looking at her.

The Paris Salon of 1861 was not amused. Critics called it pornography, and worse than that, in their view, they accused Gérôme of dragging an ancient subject down into the present and making it banal. He had worked partly from photographs: the model was Marie-Christine Leroux, and Gérôme commissioned the photographer Nadar to shoot her so that he could paint from the prints.

One correction, since the title is on the wall next to you. The ancient sources that describe this trial do not put it in front of the Areopagus at all. The comic playwright Posidippus set it in the Heliaia. The Areopagus is Gérôme's, and it sounds better.

The scandal made the painting famous. It was engraved, copied and mocked for the rest of the century. In 1884 the American cartoonist Bernhard Gillam redrew it for Puck magazine as Phryne before the Chicago Tribunal, standing the scandal-covered presidential candidate James Blaine where she stands and the newspaper editor Whitelaw Reid where Hypereides stands. The picture itself reached Hamburg by a quieter route. A London banker born in this city, John Henry Schröder, bought it from a dealer in 1866 and left it to the Kunsthalle in 1910, in the same bequest that brought the Bernini bust you will meet downstairs.

Marble does not get pockmarks, and this marble has them. Look at the two small hollows flanking his nose, and at the stubble cut into the cheeks and the chin. A twenty-five-year-old carved that.

The man is Alessandro Damasceni Peretti Montalto, made a cardinal at fifteen by his great-uncle, Pope Sixtus the Fifth. He grew into a serious patron of the arts and a well-liked figure in the politics of the papal states, and he sat for this bust shortly before his death. He died in 1623, a few months after it was finished. Gian Lorenzo Bernini had already built him a fountain of Neptune and Triton for the gardens of his villa outside Rome. Bernini's rise to becoming the sculptor of Baroque Rome had barely begun.

Look at what the stone is doing. The chest turns one way, the head turns back, and the folds of the short shoulder cape, the mozzetta, move with it. The Kunsthalle describes the aim without embarrassment: to bring a marble bust to life, which is what sculptors have taken as their own particular task ever since the story of Pygmalion. The surface was polished to a high gloss when it was new, so it answered the faintest change of light in the room. Walk round it and it is a different face from either side.

Then it vanished for nearly three centuries. It is recorded at the Villa Montalto in the early 1660s and in the Casa Peretti in 1682, and after that the trail goes cold. When Rudolf Wittkower published the standard catalogue of Bernini's sculpture in 1955, this bust is not in it, because as far as scholarship was concerned it no longer existed.

It had been in Hamburg since 1910. A banker called John Henry Schröder, born Johann Heinrich Schröder in this city, had gone to London, taken over the family bank, anglicised his name and built a collection. Sixty-three paintings and eight sculptures came to the Kunsthalle from it, forty-eight of which the museum still owns, and one of those is the Gérôme upstairs. The bust sat here, unremarked, until 1983, when it was recognised as an early masterpiece by Bernini.

One thing is still unsettled. Scholars have argued that it was made for a tomb, which would account for the bare head and the inward look, and would mean the memorial tablet it was meant to stand beside was never carved. The only setting anyone can actually document for it is the villa.