The construction of the stone castle in Niasvizh is connected with the activity of Mikołaj Krzysztof Radziwiłł Sierotka (the Orphan). He decided that the princely residence was supposed to look like a powerful fortress, conform to the modern fortification requirements and demonstrate the grandeur of the Radziwiłł family. That’s why instead of rebuilding the old wooden castle the prince began to build a new one on a peninsula made up of two artificial lakes on the river Usha.
After the castle had been robbed in 1812 by the Russian army there came a long period of decline. For almost half a century the Radziwiłłs hadn’t lived in their residence. Only in 1865 they came from Berlin to their ancestors’ land for the first time. Maria Dorota Radziwiłł wrote in her memoirs:
«When I arrived at the castle, I found a real decline! Even the moats around the castle were filled with piles of rubbish as high as the mounds ... The castle was impossible to live in. There were holes in the roofs, water all over the place, the ceilings fell in some places, some of them were nearly destroyed, the stones the yard was paved with were turned out in many places, and everything was unbelievably dirty. But despite this all I saw that the castle was possible to revive...»
Maria Dorota brought the Radziwiłłs’ residence back to life. The hall interiors were restored, some collections returned, in particular the family relics that had been brought out to the Hermitage.
The work began in 1582–1583 and the biggest part had been over by 1600. There is no consensus on who the author of the project was. It was considered that an Italian architect Yan Maria Bernardoni was in charge of the work, however, contemporary researchers say only about his participation in the construction at some stages. There is a possibility that Mikołaj Krzysztof Radziwiłł worked out the project himself, as he was really interested in architecture.
The castle became one of the best fortresses in the Great Duchy of Lithuania. On the plan it looked like a quadrilateral surrounded by a high mound with bastions on the corners and a moat with water. The princely palace was constructed opposite the entry gate, with an armoury and «kamenitsa» with a watchtower. In the castle there were also barracks, a prison, foundry, storehouses with food, and a bakery. One could get to the fortress across a wooden bridge which could be easily disassembled when necessary. There were around 30 weapons on the bastions which allowed the defenders to control the nearby territory. It all made the castle impossible to attack.
In 1660 the fortress survived the siege of the Moscow army which greatly affected the course of the war. Near Lachovichi Niasvizh drew part of the enemy squads upon itself and staved off the threat that was hanging over Slutsk. Taking into account the role of the castle in those events, the town was exempted from taxes and military quartering by the Sejm of the Polish-Lithuanian Commonwealth for 4 years.
During the Northern War in 1706 the Swedish army headed by Charles ХІІ approached the castle. The commandant being in charge of just a small squad of professional military men accepted the King’s ultimatum and opened the gate. The Swedish army robbed the castle and ruined its fortifications: the mounds were destroyed, the bastions were blown up, and the buildings were burnt up.
Reconstruction work began in the 1720s in the times of Michał Kazimierz Radziwiłł Rybońka. The rebuilt palace, and buildings of the armoury and kamenitsa were joined by galleries. At the same time the defensive function became unimportant. Now the princely residence was first of all the centre of the cultural life. There was a Theatre Hall in the palace, the chapel of Our Lady of Loreto, and a printing house for some time. The palace had a rich library, portrait gallery, weapon and suit of armour collections, a coin and medal collection. Architects Casimir Zhdanovich, Maurizio Pedetti and others worked in the castle. The King hall was made in 1784 specially for the arrival of King Stanisław August Poniatowski.
During World War I and the revolutionary events afterwards the castle wasn’t badly damaged. In the times of the Polish-Lithuanian Commonwealth it became a centre of public life for a short period. In 1926 it was visited by Marshal Józef Piłsudski. At an official reception he raised a toast to the Radziwiłł family: «to stay as eternal as these old walls».
In 1939 after the establishment of Soviet rule the fate of the castle was unclear for a long time. It was planned to open a museum, road transport technical school, or a holiday house here. The collections, library, archives were transferred to different institutions, and their big part was lost. During the German occupation there was a military hospital in the castle. After the liberation in 1944 it was decided to turn the castle into a sanatorium which functioned until 2001.
In 1993 the government of the Republic of Belarus adopted a regulation to create the museum and reserve Niasvizh, the palace restoration plan was worked out and approved. On 15 July 2005 Architectural, Residential and Cultural complex of the Radziwiłł family was put on the UNESCO world heritage list as «an outstanding example of an architectural ensemble illustrating a remarkable period of the history of humankind.» After the restoration work had been finished in July 2012 the exposition of the museum and reserve Niasvizh was opened to the public.