It is the most prominent monument of bastion castles in Lithuania. The castle was built in 1586-1589 to counter attacks of Swedes. Its construction was funded by Krzysztof Mikołaj "Perkūnas" Radziwiłł. Unfortunately, the castle was twice taken over by Swedes.
After recapturing Biržai, the noble Radziwiłł family has restored the castle in 1655-1669, they have rebuilt it according to the project of the Master Ulrich T. Spinowski. In preparation to fight the Great Northern War, the King of the Polish–Lithuanian Commonwealth Augustus II and the Russian Tsar Peter the Great signed an agreement in 1701 in Birzai Castle for the fight against Swedes. Swedes have once again attacked the castle in 1704 and have blown it up. Only a part of the walls, basements of the castle, the castle gate bridge, and ditches remained. The castle and the palace itself was rebuilt in 1978-1986 according to the project of an architect E. Purlys. Biržai Region Museum and library were established in both buildings. The castle serves as a venue of various concerts and exhibitions.
