The Olyka Castle was the principal seat of the Radziwill

Radziwill

The Radziwiłł family is an noble family of Lithuanian origin. The descendants of Kristinas Astikas, a close associate of the 14th century Lithuanian ruler Vytautas, were highly prominent for centuries, first in the Grand Duchy of Lithuania, later in the Polish-Lithuanian Commonwealth and the...

 princely family in Volhynia

Volhynia

Volhynia, Volynia, or Volyn is a historic region in western Ukraine located between the rivers Prypiat and Southern Bug River, to the north of Galicia and Podolia; the region is named for the former city of Volyn or Velyn, said to have been located on the Southern Bug River, whose name may come...

 from 1564 until the late 18th century. The founder of the castle was Prince Mikołaj "the Black" Radziwiłł (1515–1565) who gave Olyka

Olyka

Olyka is a town in Ukraine in the region of Volhynia. It is located east of Lutsk on the Putilovka river and has approximately 3,800 inhabitants .- History :...

 to his youngest son Stanisław. Two senior branches of the Radziwill family were based in Nesvizh and Kletsk

Kletsk

Kletsk is a city in the Minsk voblast of Belarus, located on the Lan river. , it had ca. 10,000 inhabitants.- History :The town was founded in 11th century by the Dregovichs, who erected a large fort and a tribal centre there...

.

The Olyka Castle was immensely influential as the first square fort with corner bastion

Bastion

A bastion, or a bulwark, is a structure projecting outward from the main enclosure of a fortification, situated in both corners of a straight wall , facilitating active defence against assaulting troops...

s in the Kresy

Kresy

The Polish term Kresy refers to a land considered by Poles as historical eastern provinces of their country. Today, it makes western Ukraine, western Belarus, as well as eastern Lithuania, with such major cities, as Lviv, Vilnius, and Hrodna. This territory belonged to the Polish-Lithuanian...

 and the prototype of many similar structures found in Eastern Europe. It was almost continuously under construction for eight decades and sustained numerous sieges between 1591 and 1648.

During Napoleon's invasion of Russia a Russian military hospital

Hospital

A hospital is a health care institution providing patient treatment by specialized staff and equipment. Hospitals often, but not always, provide for inpatient care or longer-term patient stays....

 moved in and continued in use until 1837. A 1840 document refers to the castle as untenanted. In 1883, a campaign of restoration was launched but it was not taken to its conclusion until after the First World War.

The Olyka Castle comprises four residential buildings of unequal height, forming a court in the middle and encircled by a moat

Moat

A moat is a deep, broad ditch, either dry or filled with water, that surrounds a castle, other building or town, historically to provide it with a preliminary line of defence. In some places moats evolved into more extensive water defences, including natural or artificial lakes, dams and sluices...

. The towers of the original castle have crumbled to the ground, but the network of bastions is still in place. The main palace of three storeys, although originally built in the 16th century, is essentially the upshot of renovations carried out in the 17th and 18th centuries.

Other buildings of the castle complex include a 17th-century gateway, a two-storey clock tower, and the Collegiate Church of the Holy Trinity (1635–1640), an elaborate replica of Il Gesu.