Siemowit I of Masovia

Siemowit I, Duke of Masovia by Jan Matejko

Siemowit I of Masovia (Polish: Siemowit (Ziemowit) I mazowiecki) (c. 1215 – June 23, 1262 ^[1]) was a son of Konrad I of Masovia and his wife Agafia, daughter of Svyatoslav III Igorevich.

Siemowit was: Duke of Czersk (1247–1248), Duke of Masovia (1248–1262) and Duke of Sieradz (1259–1260). He was a member of the House of Piast.

Life

His father died on August 31, 1247, leaving a legacy of the duchies of Sieradz, Łęczyca and Czersk. His brother, Casimir was already Duke of Kuyavia. Siemowit received Sieradz, Łęczyca and Czersk. Siemowit managed to keep Czersk through military aid from his other brother, Boleslaw I of Masovia.

The geopolitics of the region changed abruptly in the spring of 1248, following the sudden death of Boleslaw I of Masovia. Boleslaw left all his lands to Siemowit rather than the brother closer in age, Casimir. Taking advantage of the confusion following the death of Boleslaw, Casimir seized the stronghold of Dobrzyń nad Wisłą. Having inherited Masovia, Siemowit gave Sieradz and Łęczyca to Casimir so he could focus on Masovia's military activities on the border with the Yotvingians and Teutonic Order.

Faced with the constant raids of Baltic tribes on his territory, Siemowit made an alliance with Daniel of Galicia who suffered the same problem. Siemowit married Daniel's daughter, Pereyaslava. In 1248, Siemowit associated with Boleslaw V the Chaste, Daniel and Casimir, to organize the first major military campaign against the Yotvingians. The victory removed the threat of the Yotvingians for a few years. The allies held other military campaigns against the Yotvingians in 1253 and 1255.

Siemowit and Daniel Galicia felt they were not strong enough to face the threats of the Pagans from place such as Lithuania. In 1254 they made an agreement with the Teutonic Order. In exchange for their help, the Teutonic Order was entitled to one third of the Yotvingians' land that Siemowit had taken. This agreement was followed by a second in 1257 and a third in 1260.

This close collaboration between Siemowit and the Teutonic Order (Siemowit takes their defense before Pope Alexander IV accuses them of cruelty in 1258) was not as effective as thought. Siemowit was still targeting the Baltic tribes, while the Teutonic Knights received their territorial conquests.

Another problem that has plagued Siemowit's reign was the relationship with his brother Casimir, who feared that Siemowit's alliance with the Teutonic Knights was to strengthen Siemowit's forces so he would be able to go to war against Casimir. So Casimir captured his brother and held him prisoner. Siemowit was released the following year, following the intervention of Bolesław V the Chaste and others who promised to support Casimir against the Duchy of Pomerania.

The aggressive policy pursued by Casimir turned sour in 1259 when Boleslaw the Pious, ally of Pomerania, set up a coalition against him with Boleslaw V the Shy, Siemowit and Daniel of Galicia. The victory allowed Siemowit to recover the duchy of Sieradz. In 1260, Siemowit offered the Duchy to the eldest son of Casimir, Leszek II the Black.

After the "pacification" of the Yotvingians, another threat began to loom over Masovia from their powerful neighbour, Lithuania.

In spring 1262 Lithuania launched a major, offensiv campaign against the duchy of Mazovia. The capital, Płock was burned by Lithuanians who crossed the Vistula and captured the stronghold of Jazdów. Siemowit was killed in battle against the Lithuanians on June 23, 1262.^[2][3]

Marriage and children

Siemowit married in 1248 to Pereyaslava,^[4] daughter of Daniel of Galicia. They had three children:^[5]

1. Konrad II of Masovia (1248/1250 – 23 June 1294), Prince of Masovia
2. Boleslaus II of Masovia (after 1251 – 20 April 1313), Prince of Masovia, married Kunigunde of Bohemia and had issue^[6]
3. Salomea (d. 1301), nun

References