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 ("verse about illustrious men of the
diocese of Thérouanne who took part in the Holy Expedition"), written by an unknown author who was one of his contemporaries : The author writes
nostris diebus ("it happened nowadays"). 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. The author writes :"
Par Belramensis, fit princeps Caesariensis Eustachius notus miles, cognomine Gernirs"
William of Tyre, who was contemporary of Eustace Grenier, indicates him as one of the barons of
Baldwin of Boulogne. In the 16th century, Nicolas Despars (
Chronicles of Flanders) and Jacques Meyer (
Annals of Flanders) mention Eustace Garnier or Grenier in their lists of the Flemish knights who took an active part in the First Crusade. Jacques Meyer in his
Annals of Flanders (1561) mentions that Eustace Grenier was from the
diocese of Thérouanne. In the 16th century,
Charles du Fresne, sieur du Cange writes : « I find several families with this name of Granier or Grenier in France (…) It is difficult to guess whether Eustache was originally from Aquitaine or Picardy, or even from Flanders, as Meyer wants and who gives him the nickname of Beccam, without I know why. He calls him Beccamensis, that is to say native of Beccam, place which was to be in Flanders or in the neighbouring areas, since the author notes that Godefroi of Bouillon, in the distribution of the conquered places made to the crusader barons, did not forget his compatriots. But we can’t find a town or a village called Beccam. 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 ». In 1865, Paul Edouard Didier Riant, writes that Eustache Grenier is "one of the Flemish vassals" of the king
Baldwin I of Jerusalem. 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. ;Contemporary sources about Eustace Grenier' origins Joseph Ringel in
Césarée de Palestine: étude historique et archéologique (1975) writes : "around 1108, the Flemish knight Eustache Granier received Caesarea in fief". Jean Richard in
The Latin Kingdom of Jerusalem (1979) writes that Eustace Garnier was from the ) and one of the most loyal companions of
Baldwin I of Jerusalem. 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". 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." According to his analysis of the text and his research, Eustace Granier was a military official in the castle of
Beaurainville in the
County of Saint-Pol. He was a
rear-vassal of
Eustace III of Boulogne, because the counts of Saint-Pol held Beaurainville in fief from the
counts of Boulogne. Eustace's surname implies that either Eustace or one of his ancestors was responsible for the management of a store-house. Alan V. Murray says, Eustace most probably came to the
Holy Land in the retinue of his lord,
Hugh II of Saint-Pol, during the
First Crusade.
Jonathan Riley-Smith writes that Eustace arrived to the Kingdom of Jerusalem after 1099. Susan B. Edgington in
Albert of Aachen (2007) agrees with this analysis. She writes that Eustace Grenier probably came from Beaurain-Château in the
County of Saint-Pol. ==In the Kingdom of Jerusalem==