Biržai Castle

The castle’s ground plan is defined by an earthen bastion layout surrounded by deep water channels and sited beside Lake Širvėna at the confluence of the Apaščia and Agluona rivers. Archaeological evidence confirms that the original late sixteenth‑century design followed Italian Renaissance fortification principles, employing raised earth ramparts with projecting angular bastions and water-filled ditches as the primary defensive elements.

The defensive works comprised earth embankments faced by an upper stone wall whose top served as a parapet and battlement, while the bastions contained casemates set in two and three storeys. These features date to the 1586–1589 construction and were extensively repaired during the major mid‑seventeenth‑century rebuilding that altered the layout toward a Dutch bastion arrangement. The 1637 program repaired the dam and embankments and rebuilt the gate and bridge; the mid‑seventeenth‑century gates were described as two‑storey structures with open loggias richly finished with sculpture, carved wood and painted surfaces. After the 1704 demolition these defensive elements survive in varying condition, and later conservation has stabilised and in some places reconstructed sections of the fortification system.

Within the fortress courtyard the principal civil structures included a two‑storey gatehouse originally topped by a spire, a three‑storey princely palace and a church. Documentary and archaeological evidence records more than twenty buildings of different functions clustered inside the ramparts. The palace built or rebuilt between 1662 and 1669 is rectangular and symmetrical, measuring about 24.9 metres across and 71.1 metres in length, with outer walls roughly 1.3 metres thick and internal partitions about 1.2 metres thick. It rose two storeys with three‑storey projecting end sections and a central two‑tier arcaded gallery on the main face, and its roofline featured hipped end projections and small turrets with spires. Interior finishes of the seventeenth century included decorative stucco ceilings, painted plafond panels, glazed tiles bearing ornamental motifs and Radziwiłł heraldry, and the palace once contained a large collection of paintings and sculptures.

Surviving structural fabric after the 1704 destruction included the palace ruins, notably the southern wall, fragments of the gate building and the foundations of the arsenal and other service buildings. Conservation and restoration in the twentieth and early twenty‑first centuries have repaired and in some places reconstructed palace interiors, restored a seventeenth‑century oven in one hall and rebuilt the arsenal in 2013, so that archaeological remains and reconstructed elements now coexist on the site. The castle grounds were reorganised into a park in the late nineteenth and early twentieth centuries, a landscaped area of roughly eight hectares sloping down toward Lake Širvėna, with historic promenades and planted walks forming part of the surviving ensemble.