Casimir I of Kuyavia

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.

Casimir I of Kuyavia's Seal.

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.

In the meanwhile, Casimir I face more internal problems. In 1258 Bolesław the Pious, allied with Wartislaw III, Duke of Pomerania attacked Kujawy, demanding the return of the castellany of Ląd, who under his opinion was unlawfully transferred by Henry II the Pious to his son-in-law. The expedition was only partially successful, so that in the following year the Duke of Greater Poland organized a powerful coalition with Bolesław V the Chaste, Siemowit I and Daniel of Halych against Casimir I. The expedition was a complete victory, and on 29 November 1259, Casimir I was forced to surrender and promised to give Ląd to Bolesław the Pious.

However, Casimir I refused to return Ląd, and this caused that in 1261 the coalition attacked again. Taking advantage of his father's difficult position, Casimir I's eldest son Leszek II the Black demanded his own district, using as excuse the intrigues of his stepmother, who wanted to obtain more domains for her own children. Finally, Casimir I was forced not only to surrender the castellany of Ląd, but also gave Sieradz to his son as a separate district.

Casimir died on 14 December 1267 and was buried in the Cathedral of Włocławek.

Around 1230/31 Casimir I married firstly with Hedwig (1218/20 – 8 January aft. 1234), probably the daughter of Władysław Odonic. They had no children.

In 1239 Casimir I married secondly with Constance (c. 1221/27 – c. 21 February 1257), a daughter of Henry II the Pious. As her dowry, she received the castellany of Ląd, who was the cause of the long conflict with the Duchy of Greater Poland. They had two sons:

1. Leszek II the Black (c. 1240/42 – 30 September 1288).
2. Ziemomysł (c. 1241/45 – 29 October/24 December 1287).

In 1257, Casimir I married thirdly with Euphrosyne (c. 1228/30 – 4 November 1292), daughter of Casimir I of Opole. As her dowry, she received the district of Ruda, but the quick action of Przemysł I caused that this land never passed to the Masovian branch. They had four children:

1. Władysław I the Elbow-high (3 March 1260/19 January 1261 – 2 March 1333), King of Poland (1320–1333).
2. Casimir II (c. 1261/62 – 10 June 1294), killed in battle against the Lithuanians.
3. Siemowit (c. 1262/67 – 1312).
4. Euphemia (c. 1265 – 18 March 1308), married Yuri I of Galicia.