CASTELNAU', MICHEL DE, SIEUR DE LA MAUVISSIhRE, 1520-92; a French Soldier and ambassador to the court of queen Elizabeth. He was thoroughly educated, traveled much, and served in the French army in active service in Italy, where his courage and ability secured for him the friemiship of the cardinal of Lorraine, who took him into his service. In 1557, he was given a command in the navy, but soon rejoined the French army in Picardy. He executed several delicate diplomatic commissions so satis factorily to the constable de Montmorency that he was sent by the king to Henry II. of Scotland with dispatches for Mary Stuart, who was then betrothed to the dauphin (afterwards Francis II). He went also to England and treated with Elizabeth respect ing her claims in Calais, a settlement of which was made at the congress of Cambray. Afterwards he was sent to Margaret of Parma, governess of the Netherlands, and later still to Rome to ascertain the views of the pope with regard to France. Returning to France he again entered the navy and had the fortune to discover the earliest symptoms of the conspiracy of Amboise. After the death of Francis II. he accompanied the queen (Mary Stuart) to Scotland, remainin a year, during which time he made several journeys to England and attempted to bring about a reconciliation between Mary and Elizabeth, but his wise and temperate counsels were disregarded. In 1562, he retired to France in consequence of the civil war, and was employed against the Protest ants of Brittany, by whom he was taken prisoner, hut was soon afterwards exchanged.
He served at the siege of Rouen and at the battle of Dreux, took possession of Tanker ville, and contributed in 1563 to the recapture of Ilavre from the English. Within the next ten years he was employed in a number of important missions; first to queen Eliza beth to negotiate a peace; next to the duke of Alva, the new governor of the Nether lands, on which occasion he discovered the project formed by Conde and Coligny to seize and carry off the royal family (1567). After the battle of St. Denis he was again sent to Germany to solicit aid against the Protestants, and on his return was made gov ernor of St. Dizicr. In 157'3, he was .sent to England by Charles LX..to allay the excite meat caused by the massacre of St. Bartholomew, and in the same year was sent to Germany and Switzerland. Two years later he was sent by Henry III. as ambassador to queen Elizabeth's court, where he remained ten years. While on this duty, with a view of strengthening and maintaining the alliance between the two countries he used his influence to procure the marriage of Elizabeth with the duke of Alcucon; but Eliza beth made so many promises, only to break them, that C. at last refused to trans mit them to his government. On returning to France he was out of favor with the league, lost his governorship of St. Dizier, and was reduced to extreme destitution; but on the accession of Henry IV. he was, though a Roman Catholic, intrusted with many important missions. The memoirs of C. are valuable for their accuracy and impartiality.