Karl Rossi created a unique ensemble in the center of St. Petersburg at Palace Square, combining the baroque Winter Palace and the classically strict Main Headquarters. These buildings harmoniously complemented each other: the simplicity and elegance of the Main Headquarters emphasized the festivity and rich decor of the Winter Palace, which remained the focus as the imperial residence. Today, the headquarters building is part of the Hermitage.

In the 18th century, a large meadow was located where Palace Square now stands, and from the palace windows, there was a view of the backyards of houses facing Nevsky Prospect. On holidays, feasts for the people were held here. Rastrelli planned to transform this space into the main square, but his project was not realized. At the end of the 18th century, Y.M. Felten won a competition to design the square and built three houses for officials, but they only closed off part of the space.

After the victory over Napoleon, Alexander I decided to once again address the design of the square to emphasize Russia's status as a victor. It was decided to build the Main Headquarters in front of the Winter Palace, symbolizing the military power of the country. The project was entrusted to Karl Rossi, who was skilled at creating architectural ensembles from buildings of different styles and eras.

Rossi used several techniques to create a unified ensemble. Externally, the square appears symmetrical, and the arch of the Main Headquarters divides the building in half. The architect reconstructed Bolshaya Morskaya Street, making it the main 'gate' of the square, and erected three arches, creating the illusion of straight lines. Columns divided the facade of the headquarters into sections, giving it symmetry. The western part of the building is longer than the eastern, so it is adorned with 14 columns, while the eastern has 12.

The Main Headquarters is attributed to classicism and empire style, where one style continues the other. The facade of the building is executed in classical traditions, while the triumphal arch, in the empire style, emphasizes the grandeur of the empire. To construct the headquarters, it was necessary to buy out the houses that stood on this site, for which significant sums were paid to the owners.

Construction lasted from 1819 to 1829. Rossi utilized existing buildings, uniting them into a single structure, and erected the eastern wing for ministries. He preserved the works of his predecessors, including the halls with paintings by Quarenghi and the staircase from the Lanskoy house.

The triumphal arch became a connecting element of the complex, uniting the two wings of the headquarters. It is adorned with a sculptural composition featuring the goddess of Victory on a chariot. The sculptures are made of copper and weigh 16 tons. The architect was confident in the strength of the arch and even stood on it while scaffolding was being removed.

The authors of the sculptural group, Pimenov and Demut-Malinovsky, worked with Rossi on other projects. The sharp corner of the building facing the Moika River was nicknamed the 'iron,' and soon such 'irons' appeared in other parts of the city.

Initially, the Main Headquarters was gray with white decorations, but it was later repainted yellow, and the sculptures became black. These colors were approved by Alexander II as state colors.

In 1905, at the initiative of Mendeleev, electric clocks were installed on the arch, which were restored by the Swiss firm 'Moser.' The architect also used light lanterns to illuminate windowless rooms.

Nicholas I wanted to install a monument to Peter I in the square, but Rossi insisted on a monument in honor of the Patriotic War of 1812. The Alexander Column completed the appearance of the square. The building of the Guard Corps Headquarters became the last element of the ensemble.

The Main Headquarters consisted of a complex of offices, libraries, and apartments. There was a chapel and safe rooms for archives. Each department had a separate entrance. Receptions and events were held in the ministers' apartments.

Finance Minister Gurev, known for his bribery, sought an apartment with a view of the Winter Palace. His son-in-law, Karl Nesselrode, headed the Ministry of Foreign Affairs for over 30 years. Diplomatic negotiations were held in his apartments. Leskov ironically altered his surname to 'Kiselvrode' in 'Lefty.' Now his apartment is a museum.

Nesselrode hosted receptions to which all of Petersburg's elite were invited. The minister's wife disliked Pushkin, and he composed epigrams about her. She maintained relations with Dantes, the poet's murderer. Nesselrode was Pushkin's superior at the Collegium of Foreign Affairs.

Gurev was succeeded by Kankrin, who was known for his modesty and discipline. He walked to work and played the violin in his office, which is now also a museum.

The headquarters building has many secret rooms. Visitors can enter the museum through the former carriage gates. The grand staircase is adorned with monuments to Peter I and military leaders, cast from bronze cannons.

After the revolution, the headquarters building suffered from fires and bombings. The western wing still belongs to the military, while the eastern was given to the Hermitage. In 2008, reconstruction began, and by the 250th anniversary of the Hermitage, the building was opened.

Restorers recreated the interiors, including the stoves and Nesselrode's apartment. The inner courtyards were converted into atriums. For the first time in Russia, 'light traps' were installed here, safe for exhibits.

On the first floor, there are ticket offices and a cloakroom. On the second, exhibitions dedicated to the Ministry of Finance, Art Nouveau, African art, and Italian sculpture. On the third, the Guards Museum, Fabergé halls, empire style, Western European art, and Russian painting. On the fourth, Western art of the 20th century, Rodin sculptures, and a collectors' gallery.

In one building, modern exhibition space and the museum of Russian history are combined. The updated Main Headquarters of the Hermitage allows visitors to enjoy art without fatigue and loss of interest.