In 1310, when his father was still alive Trojden received the small region Czersk.
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When his father died in 1313 he inherited parts of Warsaw and Liw in addition to his duchy, which allowed Trojden to reign over Eastern Masovia.
By 1321, Casimir I married Euphemia (b. 1310 – d. aft. 11 January 1374), daughter of Duke Trojden I of Czersk-Warsaw.
She was the fourth daughter and youngest child of Casimir I, Duke of Cieszyn, by his wife Euphemia, daughter of Duke Trojden I of Czersk-Warsaw.
In 1326 the Grand Master formed an anti-Polish coalition at Brodnica, consisting of the Masovian dukes Siemowit II, Trojden I and Wenceslaus of Płock as well as of several Silesian Piasts and King John of Bohemia.