Upon the death of his descendant Duke Bolesław III Wrymouth in 1138, it was allocated to the newly established Duchy of Masovia, a provincial duchy of Poland.
əpˌɑːn ðə dˈɛθ ʌv hɪz dᵻsˈɛndənt dˈuːk bˈɑːlslɔː ɹˌoʊmən θɹˈiː ɹˈaɪməθ ɪn wˈʌn θˈaʊzənd wˈʌnhˈʌndɹɪd θˈɜːɾi ˈeɪt, ɪt wʌz ˈæləkˌeɪɾᵻd tə ðə nˈuːli ɪstˈæblɪʃt dˈʌtʃi ʌv mæsˈoʊviə, ɐ pɹəvˈɪnʃəl dˈʌtʃi ʌv pˈoʊlənd.