Agafia Svyatoslavna of Rus (between 1190 and 1195 – after 2 June 1248) was Princess of Masovia by her marriage to Duke Konrad I.

[1] The marriage was for political reasons, as her father had become an ally of Leszek I the White and wanted to improve relations with the Polish nobility.

It started when their son Casimir married Constance, daughter of Henry II the Pious.

Jan Długosz wrote: "And when he died his body was removed from the gallows and several brothers of a Dominican took him away to be buried.

The church bells were silent over Masovia and the citizens did not go to celebrate mass; there were also no funerals or weddings.