Duke of Masovia (Polish: Książę Mazowsza) was a title borne by the sons and descendants of the Polish Duke Bolesław III Wrymouth.^[1] In accordance with the last will and testament of Bolesław, upon his death his lands were divided into four to five hereditary provinces distributed among his sons, and a royal province of Kraków reserved for the eldest, who was to be High Duke of all Poland. This was known as the fragmentation of Poland. Subsequent developments lead to further splintering of the duchies.

The following is a list of all rulers of the Duchy of Masovia and its parts. Although not all incumbents listed here had titular rights to the title of Duke of Masovia, they are all listed as such for simplicity's sake.

Also take note that some of the dates are merely approximate and the ownership of certain lands might be disputed. Finally, this table does not include lands ruled by dukes of other parts of partitioned Poland or Wenceslaus II and Wenceslaus III.

Duchy of Masovia

Partitions of Masovia

The Duchy went through various border changes in the coming years, sometimes losing and sometimes gaining territory.

Dukes of Masovia

Piast Dynasty

Ruler		Born	Reign	Death	Ruling Part	Consort	Notes
Boleslaus (I) the Curly		1125	1138-1173	5 January 1173	Masovia	Viacheslava Vsevolodovna of Novgorod 1138 three children Maria after 1160 no children	Son of Bolesław III Wrymouth of Poland. Also Duke of Silesia and monarch of Poland.
Leszek I		1162	1173-1186	1186	Masovia	Unmarried	Son of Bolesław the Curly.
Casimir (II) the Just		1138	1186-1194	5 May 1194	Masovia	Helen of Znojmo 1163 seven children	Son of Bolesław III Wrymouth of Poland. Also monarch of Poland.
Regency of Helen of Znojmo (1194-1200)							Son of Casimir the Just. Also monarch of Poland, after his abdication of Masovia to his brother Conrad, in 1200, shortly after reaching majority.
Leszek II the White		1184/5	1194-1200	24 November 1227	Masovia	Grimislava Ingvarevna of Lutsk between 1208 and 1211 three children
Conrad I		1187/8	1200-1247	31 August 1247	Masovia	Agafia Yaroslavna of Peremyshl between 1207 and 1210 ten children	Son of Casimir the Just. Also monarch of Poland.
Boleslaus I		1208	1247-1248	25 February 1248	Masovia	Gertrude of Lower Silesia 1232 no children Anastasia Alexandrovna of Belz between 1245 and July 1247 no children	Son of Conrad I. Died without descendants.
Siemowit I		1224/8	1248-1262	23 June 1262	Masovia	Pereyaslava Danilovna of Halych 1248 three children	Brother of Bolesław I. Killed in a battle against the Lithuanians, who also took his heir prisoner.
Regencies of Pereyaslava Danilovna of Halych and Boleslaus, Duke of Greater Poland (1262-1264)							Released after two years of captivity. In 1275 divided the land with his brother Bolesław. After the division of the duchy he received Czersk. His death without male heirs allowed his brother to reunite the Duchy.
Conrad II		1250	1264-1275	24 June or 21 December 1294	Masovia	Hedwig of Legnica 1265/70 one child
			1275-1294		Czersk
Boleslaus II		1253/8	1275-1294	20 April 1313	Płock	Gaudemantė Sophia of Lithuania 1279 three children Kunigunde of Bohemia 1291 (divorced 1302) two children	Reunited the duchy after the death of his brother, but after his own death Masovia was divided again.
			1294-1313		Masovia
Trojden I		1284/6	1310-1341	13 March 1341	Warsaw	Maria Yurievna of Galicia-Volhynia 1309/10 four children	Son of Boleslaus II, retained Czersk during his father's lifetime. After Boleslaus' death, Trojden received more lands in inheritance and made Warsaw his new capital. Put his own son in the throne of Galicia-Volhynia.
Siemowit II		1283	1313-1345	18 February 1345	Rawa	Unmarried	Son of Boleslaus II, retained Rawa. Left no descendants and his duchy was inherited by his nephews Siemowit III and Casimir I.
Wenceslaus I		1293/7	1313-1336	23 May 1336	Płock	Dannila Elisabeth of Lithuania 1316 two children	Son of Boleslaus II, retained Płock.
Regencies of Siemowit II, Duke of Rawa and Trojden I, Duke of Warsaw (1336-1340)							Son of Wenceslaus. In 1351 Płock was annexed by the Kingdom of Poland.
Boleslaus III		1322/30	1336-1351	20 August 1351	Płock	Unmarried
Annexation to the Kingdom of Poland (1351-1370)
Casimir I		1329/31	1341-1349	26 November/5 December 1355	Warsaw	Unmarried	Sons of Trojden I, ruled jointly. In 1345 inherited Rawa. In 1349 divided the land between them: Siemowit received Warsaw and Casimir Rawa. After Casimir's death without descendants in 1355, Siemowit reunited Masovia. He also brought Płock from Poland in 1370. After his death the duchy was again divided between his sons Janusz I and Siemowit IV.
			1345-1355		Rawa
Siemowit III		1320	1341-1355	16 June 1381	Warsaw	Euphemia of Opava 1335 five children Anna of Ziębice c.1360 three children
			1345-1349		Rawa
			1355-1381		Masovia
John I the Elder		1347/52	1381-1429	8 December 1429	Warsaw	Danutė Anna of Lithuania 1371/3 four children	Son of Siemowit III, since 1386 hereditary vassal of Poland, after 1391 Duke of Podlasie. Although the division, the duchy of Czersk remained annexed to the duchy of Warsaw.
Siemowit IV the Younger		1353/6	1381-1426	21 January 1426	Płock (with Rawa)	Alexandra of Lithuania 1387 thirteen children	Son of Siemowit III. Since 1386, was an hereditary vassal of Poland, and, although having lost much of his domain to the Teutonic Order in 1382 (Wizna, Zawkrze, Płońsk), he gained other duchies (Bełz) from Poland.
Trojden II		1403/6	1426-1427	25 July 1427	Płock (with Rawa)	Unmarried	Sons of Siemowit IV, ruled jointly. In 1434 the three surviving brothers divided the land: Siemowit received Rawa, Casimir received Bełz, ad Ladislaus received Płock. The death of Siemowit and Casimir in 1442, both without descendants, allowed Ladislaus to reunite the inheritance of his father (all but Gostynin, town that remained under Siemowit V's widow's control).
Siemowit V		1389	1426-1442	17 February 1442	Rawa (since 1434)	Margareta of Opava-Ráciborz bet. 15 October 1434 and 17 February 1437 one child
Casimir II		1401/3	1426-1442	15 September 1442	Bełz (since 1434)	Margareta Szamotuły 26 June 1442 no children
Ladislaus I		1406/9	1426-1455	11/12 December 1455	Płock	Anna of Oleśnica 1444 two children
Regency of Anna of Lithuania (1429-1436)
Boleslaus IV		1421	1429-1454	10 September 1454	Warsaw	Barbara Olelkovna of Slutsk-Kapy 1440/5 ten children
Margareta of Opava-Ráciborz		1410	1442-1459	5 July 1459	Rawa (at Gostynin)	Siemowit V bet. 15 October 1434 and 17 February 1437 one child	Received Gostynin as her husband's inheritance. After her death her part rejoined Płock.
Anna of Oleśnica		c.1425	1455-1482	After 15 August 1482	Płock (in Sochaczew (1455-76); in Koło-Mszczonów (1476-82))	Ladislaus I 1444 two children	Sons of Ladislaus I, ruled jointly. In 1459 inherited Gostynin from their aunt Margareta. After their deaths, Masovia was again reunited by the sons of Boleslaus IV. Their mother Anna, besides the regency of her sons, had also an independent seat in Sochaczew (1455–76). When this land was annexed to Poland, she received Koło and Mszczonów as compensation (1476–82).
Regencies of Anna of Oleśnica and Paul Giżycki, Bishop of Płock (1455-1459)
Siemowit VI		2 January 1446	1455-1462	31 December 1461/1 January 1462	Płock	Unmarried
Ladislaus II		After 31 October 1448		27 February 1462	Płock
Regencies of Barbara Olelkovna of Slutsk-Kapy and Paul Giżycki, Bishop of Płock (1454-1462)							Sons of Boleslaus IV, ruled jointly under regency. In 1462 they inherited the rest of Masovia, reuniting the Duchy. However in 1471 they made new partitions: Casimir received Płock, however in 1475 abdicated of his lands to his brother Janusz, who hadn't any share of the land since 1471; Conrad received Czersk and Boleslaus Warsaw, which was reunited with Czersk by Conrad after Boleslaus' death in 1488. In 1495, as the last surviving brother in power, he reunited all Masovia definitely.
Casimir III		10 June 1448/8 June 1449	1454-1471	9 June 1480	Warsaw	Unmarried
			1471-1475		Płock
Boleslaus V		c.1453	1454-1488	27 April 1488	Warsaw	Anna Radzanów 20 July 1477 (morganatic, annulled 1480) no children
John II		1455	1454-1471	16 February 1495	Warsaw	Unmarried
			1475-1495		Płock
Conrad III the Red		1447/8	1454-1471 1488-1495	28 October 1503	Warsaw	Magdaena Stawrot 1468/70 (morganatic) no children Unknown bef. 20 July 1477 (morganatic, divorced 1493?) no children Anna Radziwiłł bet. 29 September 1496 and 2 April 1497 four children
			1471-1495		Czersk
			1495-1503		Masovia
Regency of Anna Radziwiłł (1503-1518)							Sons of Conrad III, ruled jointly.
John III		27 September 1502	1503-1526	9/10 March 1526	Masovia	Unmarried
Stanisław I		17 May 1501	1503-1524	8 August 1524	Masovia	Unmarried
Anna		c.1498	1526-1537	After 26 January 1557	Masovia	Stanisław Odrowąż 1536 one child	The last Masovian Piast. Sister of Stanislaus and John III. Anna was elected duchess by the nobles to maintain the independence of the Duchy. She forfeited her rights to Poland in 1537.