Brandenburg Gate audio guide,
five stops, free.

Stand far enough back on the cobbles that the whole thing fits in front of you, because you are on the side it was built to be looked at from. The gate faces the city. The wings on either side reach towards you like the arms of a forecourt, the sculpture is concentrated on this face, and the idea was never to impress people arriving from outside. It was meant to remind the people who lived in Berlin who ruled them.

The man who ordered it was Frederick William the Second of Prussia, and the architect was Carl Gotthard Langhans, head of the royal office of works. It went up between 1788 and 1791, on the site of an older customs gate, and it is the only one left of the eighteen gates Berlin last had. Its model was the Propylaea, the entrance to the Acropolis in Athens, and here is the first surprise: Langhans never went to Greece. He designed it from books, from the engravings of Julien-David Le Roy and of James Stuart and Nicholas Revett.

He also cheated on his model, on the king's orders. The king wanted as open a view as possible from the city through to the Tiergarten, so Langhans made the gate far shallower than the Greek original, and the columns slimmer and taller. Count them: twelve, six on each side, making five passages. Then look at the walls between the pairs. Those are not decoration. The slender columns alone could not have carried the weight above them, so each pair got a masonry wall to lean on.

Now look at the middle passage. It is 5.65 metres wide, the other four 3.80, and it was the royal carriageway. Until the end of the monarchy only the royal family could use it, and from 1814 the family of General Ernst von Pfuel, in thanks for bringing the Quadriga home from Paris.

The gate was first called the Friedenstor, the Peace Gate, and it was opened to traffic in August 1791 before it was even finished. The peace it celebrated was a Prussian military intervention in the Netherlands in 1787. The square you are standing in had no name at all until March 1814, when it became Pariser Platz, after the allies marched into Paris.

One more thing to take in before you walk forward. In 1945 every building around this square was rubble, and the gate was the only structure still standing. Everything you see around you was rebuilt after 1990, to rules that fixed the eaves height at 22 metres.

Walk through one of the side passages, slowly, and look up at the walls either side of you. Those carved panels are Hercules: strangling snakes as a baby, fighting centaurs, carrying off the apples of the Hesperides. There are twenty of them across the five passages, drawn by Bernhard Rode and carved by ten different sculptors. They were meant as an allegory of Frederick the Great, and Schadow himself, who oversaw them, later dismissed them as reliefs in the five passages that nobody can see. You are one of the few who has looked.

Notice too the tall recesses in the passage walls. That is where the gates folded back. In the daytime the wooden leaves stood open, so that nothing blocked the view through to the Tiergarten.

Now come out onto the square and turn round. This is the back of the gate, and it shows. The only decoration on this face is the row of square reliefs under the cornice. The attic above it is blank: a relief was planned here showing seven scattered arrows bound back into one bundle, meaning the seven Dutch provinces, and for reasons nobody knows it was never made. And look at Victoria. She is driving away from you, towards the city. Schadow had a flowing garment added to her because, he said, from behind she looked so stiff and bare.

The square has been called Platz des 18. März since June 2000, after two eighteenths of March: 1848, when hundreds of civilians died in the barricade fighting of Berlin's revolution, and 1990, East Germany's first free election. Between those two dates it had a much harder history. From 1961 this was East Berlin's border zone, and a curving section of the Wall ran round in front of the gate, reinforced as a tank barrier three metres thick. Look down at the paving. The double row of stones is its line.

On the thirteenth of August 1961 West Berliners gathered on this side to protest, the mayor Willy Brandt among them. In 1963 the Soviets hung red banners across the gate so that John F. Kennedy could not look through. Richard von Weizsäcker, as mayor, put the whole problem in one sentence: the German question is open as long as the Brandenburg Gate is closed. And on the twelfth of June 1987, in front of the Wall here, Ronald Reagan said the line everyone remembers: Mister Gorbachev, open this gate. Mister Gorbachev, tear down this wall.

The gate opened on the twenty-second of December 1989, when Helmut Kohl walked through from the west and Hans Modrow was waiting on the other side.

You are 24 metres up, on the roof of the building you were just looking at from the lawn, and the corner towers that seemed so tall from down there are now more or less at eye level. Walk to the edge of the terrace and find the Brandenburg Gate to the south-south-east. From up here you see the Quadriga side-on, driving left, east, towards the city centre, exactly as it was built to.

The Bundestag describes this roof as offering views of the parliamentary and government district and Berlin's sights, and its own guide for children names three of them: the Chancellery, the Victory Column and the gate. In the divided city, foreign state guests were routinely brought onto this building's outer terraces for one reason, to look over the Wall.

Now turn to the dome beside you. Wallot's building had a cupola too, of steel and glass, considered an engineering feat in 1894, and the emperor resented it partly because it rose higher than the 67-metre dome of his own palace. It was damaged in the fire of 1933 and again in the war, and on the twenty-second of November 1954 Soviet specialists blew up what was left of it, officially because it was unstable.

The new one very nearly did not happen. Norman Foster's design for the rebuilding had no dome at all, and he said in writing that he could not recommend any structure on the roof built for purely symbolic reasons. The politicians wanted one. The roof was redesigned several times under that pressure, and on the eighth of May 1995 Foster presented a walk-in glass dome, which the members approved. The idea of a glass dome that visitors could walk up had already been drawn years earlier, in 1988, by the architect Gottfried Böhm. So the dome is a compromise its own architect argued against.

Look at its outside. It is half an ellipsoid, 38 metres across and 23.5 metres high, and its top stands 47 metres above the ground, well below where Wallot's cupola rose. The frame is 24 vertical ribs and 17 rings, about 800 tonnes of steel carrying 3,000 square metres of glass. More than 300 square metres of solar panels on this roof help power the building.

Almost three million visitors a year come to this building, which makes it the most visited parliament building in the world. Before you go, look down over the west parapet at Platz der Republik. The big flag on the lawn is the Flag of Unity, six by ten metres, raised there at the stroke of midnight on the third of October 1990, and it still flies there.