Eustace I Granier, also known as Eustace Grenier or Eustace Garnier, called in Latin Eustachius Granarius in the charters (born around 1070 and died on 15 June 1123), was a Flemish crusader who took part in the First Crusade. He became lord of Caesarea in 1101 and lord of Sidon in 1110. On 18 April 1123, he was elected constable and bailiff of Jerusalem during the captivity of Baldwin II of Jerusalem. Shortly before his death, he defeated a Fatimid army at the Battle of Yibneh near Ibelin. Eustace Grenier is quoted in a text in verse written during his life in honour of the knights of the diocese of Thérouanne who accompanied Baldwin of Boulogne to the Holy Land. Contemporary authors and historians identify Eustace Grenier as a nobleman from the diocese of Thérouanne in the County of Saint-Pol. Alan V. Murray, historian of the Crusades, 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 Therouanne". Origins 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"), 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" (Trad) : "Peer of Belrem became prince of Caesarea Eustace famous knight, named Garnier" His name is given in Latin under different forms (Garnerius, Granerius, Granarius).

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Eustace I Granier, also known as Eustace Grenier or Eustace Garnier, called in Latin Eustachius Granarius in the charters (born around 1070 and died on 15 June 1123), was a Flemish crusader who took part in the First Crusade. He became lord of Caesarea in 1101 and lord of Sidon in 1110. On 18 April 1123, he was elected constable and bailiff of Jerusalem during the captivity of Baldwin II of Jerusalem. Shortly before his death, he defeated a Fatimid army at the Battle of Yibneh near Ibelin.