Grenier is a presumed member of the knights of the diocese of Thérouanne in the County of Saint-Pol who accompanied Baldwin of Boulogne to the Holy Land, as he is quoted in a text written during his life in their honour.
[3] Eustace Granier's place of origin is given by a poem in Latin, the Versus de viris illustribus diocesis Tarvanensis qui in sacra fuere expeditione ("vers about illustrious men of the diocese of Thérouanne who took part in the Holy Expedition"),[4] written by an unknown author who was one of his contemporaries : The author writes nostris diebus ("it happened nowadays").
[5] In this poem Eustace Grenier is cited among the knights of the Diocese of Thérouanne who accompanied Baldwin of Boulogne, the future king of Jerusalem, to the Holy Land.
Latin verses in honour of the characters from the diocese of Thérouanne who distinguished themselves in the First Crusade, tell us that Eustache, nicknamed Gernirs, became prince or lord of Caesarea ».
[13] In 1892, the abbey and historian Daniel Haigneré in Bulletin de la Société des antiquaires de la Morinie writes an article about the verse written from the time of Eustace Grenier quoting "Eustace, famous knight, named Garnier, prince of Caesarea" among the knights of the diocese of Thérouanne who accompanied Baldwin of Boulogne to the Holy Land.
[14] Joseph Ringel in Césarée de Palestine: étude historique et archéologique (1975) writes : "around 1108, the Flemish knight Eustache Granier received Caesarea in fief".
[16] Steven Tibble in Monarchy and Lordships in the Latin Kingdom of Jerusalem, 1099-1291 (1989) writes that Eustace Grenier is "a Flemish knight who had arrived in the Near East some time between 1099 and August 1105".
[17] Historian Alan V. Murray in his book The Crusader Kingdom of Jerusalem: A Dynastic History 1099-1125 (2000) writes :"However, his origins can be established with a high degree of certainty.
The Versus de viris illustribus diocesis Tarvanensis qui in sacra fuere expeditione identifies him as a Fleming from the Diocese of Thérouanne.
[22] Baldwin appointed him and Pagan of Haifa to start negotiations with Bertrand of Toulouse, William Jordan of Cerdanya and Tancred, the regent of Antioch, about the organization of a conference where they could resolve their conflicts.
[26] The assembly passed decrees that regulated the collection and spending of tithes and ordered the persecution of adultery, procuring, homosexuality, bigamy and sexual relations between Christians and Muslims.
[29] Eustace soon sent reinforcements to Kharpurt to assist the king, but Balak ibn Bahram recaptured the fortress by the time the crusader troops reached it.