Ciechanowiec (; , ) is a small town in Gmina Ciechanowiec, Wysokie Mazowieckie County, Podlaskie Voivodeship, eastern Poland. As of December 2021, the town has a population of 4,511. History In the sixteenth century the city belonged to the Kiszka family. In the mid-sixteenth century Castellan of Trakai, Piotr Kiszka built a castle on the right bank of the river Nurzec, northeast of the town. Between 1617–1642, Mikołaj Kiszka ordered to build heavy defensive walls around the fortress, but soon the castle burned down during the Deluge, and the surviving buildings with the newly built residence for the Ossoliński family were later blown up and destroyed by the Imperial Russian Army during World War I (1915). To this day only the foundations and the moat still exist. The forthcoming owners of the city were: The Bremmer, Ossoliński, Szczukow and Ciecierski families. In particular, the Ossoliński family in the second half of the seventeenth century invested in the development of the city. In 1736–1739, a brick church of the Holy Trinity and the Sisters of Mercy hospital was built, according to the draft of Warmia's architect Jan Adrian Kluk. His son, Fr. Jan Krzysztof Kluk (1739–1796), the local parish priest, devoted to natural history, became one of the most important Polish naturalists of the Enlightenment. He is the author of the first comprehensive textbook in the Polish language on agriculture, as well as other pioneering scientific topics, as well as school textbooks written on request of the Commission of National Education. The scope of the research included both botany and zoology, and natural pharmaceuticals. In the era of the partitions, Ciechanowiec was passed onto Prussia, and after the Congress of Vienna to the Russian Empire. Later the city was divided into two parts: right bank (called New Town or "Polish section"), was part of the Polish Kingdom and the left bank Old Town ("Rus section") in Russia. As a result of the November and January Uprisings, the right bank of Ciechanowiec lost the city rights in 1870. At the end of the nineteenth century, the textile industry rapidly developed in the city. Ciechanowiec was also very popular for various horse fairs. Significant damage from the times of World War I and the Polish–Soviet War were slowly repaired in the interwar period. Before the beginning of World War II, 55% of the town's inhabitants were Jews. At that time the city was