The core of the house is a one-story residential building with seven bays along the facade, built in the early 1740s. To the right of it were the gates. Its original owner was Pyotr Timofeyevich Savelov, and later it belonged to Musin-Pushkin, Razumovsky, and Morkov (under whom, in 1790, a three-story wing was built on the site of the gates).

According to other sources, the order of ownership was somewhat different: after the death of Pyotr Timofeyevich Savelov, the house was purchased by Thomas Sebek, owner of a sugar factory; then it belonged to Sergey Sergeyevich Gagarin (grandfather of the aforementioned), from 1776 to Alexey Ivanovich Musin-Pushkin, from 1780 to Pyotr Kirillovich Razumovsky, from 1787 to Arkady Ivanovich Morkov, and from 1792 to Karl Ivanovich Amburger (later also Khitrovo, de Serigny).

At the beginning of the 19th century, the house passed to the widow of Actual State Councillor Zakhar Khitrovo, Alexandra Nikolaevna, who in 1807 established a house church of the Akhtyrskaya Mother of God in the building. After her, the house went to her daughter, Sofya Zakharovna, who by her second marriage was de Serigny. In 1834, the house was bought by Monferran, who sold it for 150,000 rubles along with a renovation project to P. N. Demidov (who also owned the neighboring house, No. 43, and for whom Monferran also carried out renovations). The current appearance of the building was designed by Auguste Monferran between 1835 and 1840. The center of the right part of the building is highlighted by four columns standing close to the wall, topped by a parapet with four sculptures that seem to continue the columns. The left part of the house is a three-story wing set back into the depth of the plot, in front of which is an open terrace with marble busts on the railing; thus, the building combines three volumes of different heights. The inner courtyard is surrounded by four- and three-story wings.

This layout influenced the interiors: classicism is characterized by an enfilade arrangement of rooms, which was impossible in this building. A large hall was arranged in the right part, extended into the depth of the plot. The entrance was located at the corner of the building, which enhanced the asymmetry of the facade.

The parapet of the right part is decorated with three bas-reliefs: “Francis I at the dying Leonardo da Vinci,” “Michelangelo shows Pope Paul III the project of St. Peter’s Basilica in Rome,” and “Charles I hands Titian a brush.” Above the parapet was the sculptural Demidov coat of arms. The terrace was adorned with bas-reliefs on themes from La Fontaine’s fables: “The Hare and the Tortoise,” “The Wolf and the Sheep,”

“The Lion and the Mouse,” “The Monkey and the Dolphin,” and “Two Snakes” (these were lost and later restored).

The furniture designed by Monferran was mainly made of mahogany, as well as oak, birch, and ash by Gambs. The decoration was one of the first examples of eclecticism.

The interior decoration was altered in the 1890s. Some rooms still retain oak and walnut panels and doors, marble and carved fireplaces. The best-preserved decoration is in the vestibule: the lower part of the walls is clad with oak panels decorated with semi-circular topped panels. On the walls are rectangular panels in profiled frames; above the walls is a cornice on molded brackets. The vestibule features a white marble staircase with a gilded bronze vase-candelabrum. The railing begins with a large volute, and the floor is laid with black and white marble tiles in a checkerboard pattern.

The Great Hall has an oak gallery on three sides. The ceiling is flat, covered with patterned wood. On the ceiling are three octagonal panels with geometric patterns and the date “1890.” The panels on the ceiling are separated by triangular panels. The cornice is decorated with carved brackets with panels between them. The lower part of the walls is covered with oak panels with rectangular panels arranged in two rows; above the panels is a dark brown fabric upholstery. The paneled doors, also made of oak, are framed by Ionic carved pilasters. Above them is a pediment with brackets on the sides, featuring a carved scale-like pattern.

The house has a fireplace with a black marble slab supported by two pairs of twisted black marble columns. The firebox is lined with white tiles decorated with blue marine and architectural landscapes.

From the 1870s until 1917, the mansion was owned by Prince S. S. Gagarin and his wife, who partially rebuilt the house in 1873–1874 (destroying two doors on the left and replacing the right window with an entrance; architects were Shtrom and Mesmakher).

In 1839, Demidov ordered the driveway in front of the house to be paved with asphalt slabs laid on a layer of sand, fulfilling the obligation to maintain the pavement in front of the estate. The slabs soon began to spread apart.

In 1918, the house was confiscated in favor of the Commissariat of National Economy. In the 1920s, various institutions occupied the building, including the Leningrad Auto Club and a ballroom dance club that used the Great Hall. During the Great Patriotic War, the house housed the USSR Maritime Register.

Sources:

https://ru.wikipedia.org/wiki/Дом_Гагариной