Biržai Castle is an earth bastion-type castle. The construction started in 1586 by the order of Krzysztof Mikołaj Radziwiłł. In 1575, preparing for this construction, a dam was built on the Agluona and Apaščia rivers at their confluence, and the artificial Lake Širvėna, covering about 40 km², was created. Major castle building works were finished in 1589.
Since the second half of the 17th century, the castle has been the main seat of the Biržai-Dubingiai Radziwiłł family line, which was transferred here from the Dubingiai Castle. Biržai Castle served as a major defensive structure during the wars with Sweden.
The castle was reconstructed from ruins in the 1980s, in the Renaissance-Baroque style. The residential manor of the castle houses a library and a regional history museum 'Sėla' (literally Selonia), founded in 1928.
References:Redipuglia is the largest Italian Military Sacrarium. It rises up on the western front of the Monte Sei Busi, which, in the First World War was bitterly fought after because, although it was not very high, from its summit it allowed an ample range of access from the West to the first steps of the Karstic table area.
The monumental staircase on which the remains of one hundred thousand fallen soldiers are lined up and which has at its base the monolith of the Duke of Aosta, who was the commanding officer of the third Brigade, and gives an image of a military grouping in the field of a Great Unity with its Commanding Officer at the front. The mortal remains of 100,187 fallen soldiers lie here, 39,857 of them identified and 60,330 unknown.