Kronprinzenpalais

Listen for a moment. Behind you, traffic moves along Unter den Linden, the broad boulevard named for its lime trees. In front of you stands a pale, calm facade with tall windows in tidy rows. Columns frame the entrance, and a balcony rests above it. The building does not shout for attention. Yet some of the most important days in German history passed behind these walls, from royal births to the paperwork that reunited a divided country.

This is the Kronprinzenpalais, the Crown Prince's Palace. The name tells you its first purpose. It was the Berlin home of the heir to the Prussian throne, the young man waiting to become king. The site's history goes back to the seventeenth century, when an ordinary townhouse stood here. In the 1730s, that house was rebuilt and enlarged into a residence fit for a royal prince.

The first famous resident was a crown prince named Frederick. History remembers him as Frederick the Great. In the 1730s he was still young, recently married, and living under the strict control of his father, the soldier king Frederick William the First. This palace gave him a home of his own in the city. Later, as king, Frederick would reshape this whole stretch of Unter den Linden with an opera house, a library and a grand square.

After Frederick, the palace kept its role. Generation after generation, the heirs of the Hohenzollern family, the dynasty that ruled Prussia, lived here. King Frederick William the Third is closely linked with the house. He and his wife, Queen Louise, preferred its relative modesty to the larger royal palace nearby. Louise became one of the most loved figures in Prussian memory, and this was one of the places where she made her home.

Now look up at the top floor. Here is the first detail many visitors miss. The building you see is taller than the original. In the mid-nineteenth century, the architect Johann Heinrich Strack added a full extra storey. He also gave the facade its neoclassical style, the calm, column-framed look inspired by ancient Greece and Rome. Much of what shapes this street today comes from that same era of Prussian taste.

In 1859, a baby boy was born inside this palace. His name was Wilhelm. Decades later he became Kaiser Wilhelm the Second, the last German emperor. He led the country into the First World War. When that war ended in defeat in 1918, the monarchy fell. Wilhelm went into exile, and the palace where he was born suddenly had no royal purpose at all.

What came next is the second surprise. The new republic turned this royal home into a museum of modern art. From 1919, it housed a new department of the National Gallery, devoted to the art of its own time. Expressionist painters hung here — artists who used bold colour and distorted shapes to show emotion. For a few years, this former prince's house was one of the most forward-looking art spaces in Europe.

That openness did not last. After the Nazis took power in 1933, they attacked modern art and called it degenerate. The collection here became a target. In 1937 the modern art galleries were closed. Many works were removed, sold abroad or lost. The empty rooms carried a clear message about how quickly a society could turn against its own artists.

The Second World War brought heavy bombing to central Berlin. By 1945, the Kronprinzenpalais was largely destroyed, a burned-out shell on a ruined boulevard. After the war, this part of the city lay in the Soviet sector, and later in East Berlin, the capital of the German Democratic Republic. For years, the site stood damaged and unused, while the government decided what to save.

In the late 1960s, East German planners rebuilt the palace. They followed the outside appearance of Strack's nineteenth-century design. So the facade you see is largely a reconstruction, not the original stone. Inside, the building served the East German state as a guesthouse for official visitors. It was a curious fate for a royal home — rebuilt by a socialist government to receive foreign delegations.

Then came 1990. The Berlin Wall had fallen the year before, and the two German states moved quickly toward unity. On 31 August 1990, representatives of East and West Germany signed the Unification Treaty here, in this building. That document set out how the two countries would become one. A palace built for princes, rebuilt by a communist state, became the place where a divided nation agreed to join together again.

Before you leave, walk a few steps to the side of the building. Look for the arched bridge that crosses the narrow street. It links this palace to its neighbour, the Princesses' Palace, once home to royal daughters. Across the boulevard, you can see the State Opera and the edge of Bebelplatz. Next door stands the old arsenal, now the German Historical Museum. Together they form one of the most complete royal ensembles in Berlin.

Today the Kronprinzenpalais is used mostly for events and exhibitions, so the doors are not always open. That is fine. Much of its story is visible from the pavement. Stand back on the central walkway under the lime trees. From there you can take in the full facade, the extra top storey and the bridge at the corner in one view.

So take a last look. The windows are quiet, and the stone looks almost new. It is easy to walk past this building on the way to somewhere more famous. But this house saw a future king grow up, an emperor born, modern art celebrated and then banned, and a country made whole again. As you walk on along Unter den Linden, listen to the traffic, the footsteps and the voices. This street is still busy writing history.