Historic Berlin was a twin-city comprising of Alt-Berlin and Cölln on either side of the river Spree. Both cities were surrounded by a single defensive structure. Such twin-cities are not unique, we only have to think of Budapest, Cologne-Deutz, Nuremberg (Lorenz and Sebald), Herzogenrath-Kirchrath and Bielsko-Biala. In 1670 the Elector Fredric William I of Brandenburg granted the Cöllnischer Tiergarten west of the city walls to his wife Dorothea Sofia of Sleswick-Holstein-Sonderburg-Glücksburg. The area was deforested and streets were laid out in the following years. This Neustadt (literally: New City) was granted city rights in 1674 en was renamed Dorotheenstadt in honour of the Electress in 1781. South of Dorotheenstadt lies the second Electoral new town: Friedrichstadt named after Fredrick I of Brandenburg, King of Prussia. After the death of his father in 1688 prince-elector Fredrick (Friedrich) was granted the right to develop a new city outside of the city walls. This new city was founded in 1691 on the former floodplain of the Spree river. In 1710 the independent cities of Berlin, Cölln, Friedrichswerder, Dorotheeenstadt and Friedrichstadt were merged to form the Royal Residence and Capital City of Berlin.
In 1720 work started to construct new city defences around the united city. This meant that the old defences could be dismantled. On the site of a demolished bulwark close to the old City Palace (Altes Stadtschloss) a new ensemble of buildings was to be erected with a new Residential Palace at its core. The ensemble was aligned with the former hunting avenue of Unter den Linden, the central axis of Dorotheenstadt and comprised of a large three-winged building with two inner courtyards and a large cour d'honeur surrounded by a semi-circular colonnade. In line with the wings the architect Knobelsdorff planned an Opera House and a Ball Hall. The royal ensemble was to be free-standing on an extensive monumental square. As the important thoroughfare of Unter den Linden ran across, the Residential Square was planned as a public space from the onset.
Work started shortly after the installation of Fredrick II as the new King of Prussia in 1740. The new king ordered the purchase of 54 houses in Dorotheenstadt, among them the Palace of the Margraves of Brandenburg-Schwedt a sideline of the ruling Hohenzollern family. The waterlogged ground and difficulties in acquiring noble residences lead to adaptations to the plan. The blatant refusals of the Margaves of Brandenburg-Schwedt led to a repositioning of the Opera House and the residential palace was moved further back and made less wide so the existing city residence of the Margraves would align with the western wing. The Ball Hall was redesigned as an Academy of Science. This was the beginning of a transition from a monumental residence towards a cultural forum. The first stone for the Opera House was laid on September 5th 1741. The central square thus became known as the Opernplatz (Opera Square). The construction of the Hedwigskirche started directly after the end of the Silesian War in 1747. The residence was scaled down and in 1748 work began on the Prinz-Heinrich-Palais (Palace of Prince Henry). In 1774 the Brandenburg-Schwedt-Palais was offered for purchase and was demolished to make way for the Academy of Science. On the site of the former Royal Stables the Royal Library (Königliche Bibliothek) was built between 1775-1786.
In 1773 work had started to change the Lindenmarkt south of the Opernplatz after designs of Georg Christian Unger. The cuirassier regiment Gens d'Armes had had their barracks here. For the many French Huguenots living in Friedrichstadt a church modelled after the Huguenot temple of Charenton-Saint-Maurice was built on the Lindenmarkt between 1701-1708. At the same time the mirroring Neue Kirche (New Church) was built at the northern end of the market square. In 1785 a domed tower was added to the French Church to create a symmetrical image. In 1818 work started on building the Schauspielhaus (Theatre) between the two churches. In the same year the Neue Wache (New Watch) was added to the Forum to commemorate the Napoleonic Wars. The two squares together with the avenue of Unter den Linden structure the grid of the western elector-cities. These places became the focal point for introducing new official and representative buildings within the urban fabric of Berlin.
The name Forum Fridericianum wasn't used in the 18th century. Knobelsdorff makes a reference to the foro di frederigo. Later in the nineteenth century this term was taken up in art-historical literature , but in the Latin translation: Forum Fridericianum. The idea of a cultural forum was taken up in many capital cities as a spatial intervention on the edge of the formerly walled capital city.
Around 1800 plans are made to expand the cultural program by building new museums to showcase the artistic treasures held by the Prussian state and the Crown. This museum quarter was realised in Altkölnn (on the island of Cölln between Spree and Kupfergraben -the old city moat). The Altes Museum was built at the end of the Hofgarten at a right angle to the Stadtschloss in 1830. The Neues Museum, built directly behind the Old Museum, was finished in 1859. The Alte Nationalgalerie (Old National Gallery) was built next to this in 1876. In 1905 the baroque Supreme Parish Church was replaced with a new Cathedral: the Berliner Dom. The Pergamon Museum was finished in 1930, specifically to house treasures like the Pergamon Altar and the Ishtar Gate.
The Forum Fridericianum is located near the old residence of the Prussian rulers (1) across from the Hofgarten (Palace Gardens - 2).The hunting avenue (3) of Unter den Linden (literally: Under the Lime trees) ran from the Schlossplatz to the Tiergarten (a Deer park). It later formed the central axis of Dorotheenstadt. Within the old fortifications the Zeughaus (Arms House - 4), Kommandantenhaus (Commanders House - 5), Kronprinzenpalais (Crown Prince Palace - 6) and Kronprinzessinpalais (Crown Prinsess Palace - 7) stood. On the forum around the former Opernplatz we find the Opera House (8), the Neue Wache (9),the Prinz-Heinrich-Palais (10), the National Library (11), the Academy of Science (12) and Saint Hedwig Church (13). On the Gendarmenmarkt, the former Lindenmarkt, we find the French Church (14), the Theatre (15) and the Deutscher Dom (16). Near the Hofgarten we find the museum quarter with the Berliner Dom (17), the Altes Museum (18), the Neues Museum (19), the Alte Nationalgalerie (20) and the Pergamon Museum (21).