Siemowit I Piast of Masovia, Duke of Masovia, Duke of Czersk, Duke of Sieradz, was born circa 1213 to Konrad of Poland (c1188-1247) and Agafia of Rus (c1192-c1248) and died 23 June 1262 of unspecified causes. He married Pereyaslava Daniilovna of Halych (c1231-1283) 1248 JL . Alfred the Great (849-899)/s, Charlemagne (747-814)/s, Rollo of Normandy (860-932)/s.
|Offspring of Siemowit I of Masovia and Pereyaslava Daniilovna of Halych (c1231-1283)|
|Konrad II of Masovia (c1249-1294)||1249||1294 Czerwińsk||Hedwig of Poland (c1252-aft1280)|
|Boleslaus II of Masovia (c1251-1313)||1251||20 April 1313||Sophia of Lithuania Sophia of Lithuania Kunigunde of Bohemia (1265-1321)|
|Salomea of Masovia (?-1301)|