Balderic's most valuable work from the second part of his career is his "Historiae Hierosolymitanae libri IV", an account of the First Crusade, based in part on the testimony of eyewitnesses, and submitted for correction to the Abbot Peter of Maillezais, who had accompanied the Crusaders.
It remained the seat of the bishopric Maillezais until 1648, when the bishopric was transferred to the St. Louis Cathedral of La Rochelle.
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Maillezais Cathedral (Cathédrale Saint-Pierre de Maillezais) is a ruined Roman Catholic cathedral in the commune of Maillezais in the Vendée, France.
In 1010, Saint-Pierre-le-Vieux transferred to St. Peter Maillezais.
In 1821 a see was established at Luçon, and had under its jurisdiction, aside from the former Diocese of Luçon, almost the entire former Diocese of Maillezais; so that Maillezais, once transferred to La Rochelle, no longer belongs to the diocese, now known as La Rochelle et Saintes.
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This diocese before the French Revolution, aside from Maillezais, included the present arrondissements of Marennes, Rochefort, La Rochelle, and a part of Saint-Jean-d'Angély.