Casimir I of Kuyavia

Casimir I of Kuyavia
Casimir I of Kuyavia
Spouse(s)	Jadwiga Constance of Wrocław Euphrosyne of Opole
Noble family	House of Piast
Father	Konrad I of Masovia
Mother	Agafia of Rus
Born	c. 1211
Died	14 December 1267(1267-12-14)
Buried	Cathedral of Włocławek

Casimir I of Kuyavia (Polish: Kazimierz I kujawski) (c. 1211 – 14 December 1267), was a Polish prince member of the House of Piast, Duke of Kujawy since 1233, ruler over Ląd during 1239-1261, ruler over Wyszogród since 1242, Duke of Sieradz during 1247-1261, Duke of Łęczyca since 1247 and Duke of Dobrzyń since 1248.

He was the second son of Konrad I of Masovia and his wife Agafia of Rus. He was probably named after his grandfather, Casimir II the Just.

Casimir I received Kujawy (however without Dobrzyń and Sieradz-Łęczyca) from his father in 1233. In 1239, he would enlarge his domains with the castellany of Ląd, who received as a dowry of his second wife. In subsequent years, Casimir I actively supported his father's turbulent politics, who brought him in 1242 the conquer of the district of Wyszogród from the rulers of Gdańsk.

Konrad I died on 31 August 1247. Under his will, mostly of Masovia passed to his oldest son Bolesław I and the youngest of his sons, Siemowit I, received Sieradz-Łęczyca. Dissatisfied with his part of the paternal inheritance, Casimir I attacked his brothers (who are in Płock at the funeral of their father) and was able to conquer Siemowit I's inheritance.

The next geopolitical change in Masovia came shortly after, with the unexpected death of Bolesław I in early 1248 without issue; in his will, he left all his domains to his brother Siemowit I. In this opportunity Casimir I was able to take advantage of the confusion after his older brother's death, and capture Dobrzyń.

During the 1250s Casimir I was busy in his project to Christianize the Yotvingian tribes and establish peaceful relations with them. However his plans wasn't supported by the Teutonic Order, which had the Pope on its side. After its failure, Casimir I turned his attention elsewhere. In order to secure the northern border of his territory, he appealed to the Knights Templar, who settled in Łuków. It wasn't until 1263 that his relations with the Teutonic Order where normalized.