Isidore was an Orthodox priest of the church of Saint Nicholas in the city of Yuriev, also known as Derpt or Dorpat and now the Estonian city of Tartu. He is commemorated together with seventy-two members of his flock who were martyred with him in 1472 for refusing to abandon the Orthodox faith for Roman Catholicism. Their feast is kept on January 8.
Yuriev lay within the Livonian Confederation, a territory under the control of Roman Catholic knights. A treaty of 1463 between Ivan III of Moscow and the Livonian authorities had guaranteed protection for the Orthodox population, but according to the accounts the German Catholic authorities broke this agreement and undertook a campaign to compel the local Orthodox to convert. Isidore and his parish stood at the center of this pressure.
On the Feast of Theophany the priest and seventy-two of his parishioners went to bless the waters of the River Omovzha, also called the Emajogi, at a hole cut in the ice for the rite. There they were seized and brought before the Latin bishop Andrew and the city's civil judges, who demanded that they accept the Catholic faith. When they refused to renounce Christ and Orthodoxy, they were imprisoned and then taken back to the river and drowned through the same hole in the ice that had been opened for the blessing of the waters.
