Michel de Castelnau
Michel de Castelnau, Sieur de la Mauvissière (c. 1520–1592), French soldier and diplomat, ambassador to Queen Elizabeth.
He was born in La Mauvissière (now part of Neuvy-le-Roi, Indre-et-Loire), Touraine about 1520. He was one of a large family of children, and his grandfather, Pierre de Castelnau, was Equerry (Master of the Horse) to Louis XII. 
Endowed with a clear and penetrating intellect and remarkable strength of memory, he received a careful education, capped off with travels in Italy and a long stay at Rome. He then spent some time in Malta and afterwards entered the army. His first acquaintance with war was in the campaigns of the French in Italy. His abilities and his courage won him the friendship and protection of the cardinal of Lorraine, who took him into his service. 
In 1557 a command in the navy was given to him, and the cardinal proposed to get him knighted. This, however, he declined, and then rejoined the French army in Picardy. Various delicate missions requiring tact and discretion were entrusted to him by the constable de Montmorency, and these he discharged so satisfactorily that he was sent by the king, Henry II, to Scotland with dispatches for Mary Stuart, then betrothed to the Dauphin (afterwards Francis II). 
From Scotland he passed into England, and treated with Queen Elizabeth respecting her claims on Calais (1559), a settlement of which was effected at the congress of Le Cateau-Cambrésis. He was next sent as ambassador to the princes of Germany, for the purpose of prevailing upon them to withdraw their favor from the Protestants. This embassy was followed by missions to Margaret of Parma, governess of the Netherlands, to Savoy, and then to Rome, to ascertain the views of Pope Paul IV in regard to France. Paul having died just before his arrival, Castelnau used his influence in favor of the election of Pius IV. Returning to France, he once more entered the navy, and served under his former patron. It was his good fortune, at Nantes, to discover the earliest symptoms of the Conspiracy of Amboise, which he immediately reported to the government.
After the death of Francis II (December 1560) he accompanied the queen, Mary Stuart, to Scotland, and remained with her a year, during which time he made several journeys into England in an attempt to bring about a reconciliation between Mary and Queen Elizabeth. The wise and moderate counsel that he offered to the former were unheeded. 
In 1562, as a consequence of the civil war in France, he returned there. He was employed against the Protestants in Brittany, was taken prisoner in an engagement with them and sent to Havre, but was soon after exchanged. In the midst of the excited passions of his countrymen, Castelnau, who was a sincere Roman Catholic, maintained a wise self-control and moderation, and by his counsels rendered valuable service to the government. He served at the siege of Rouen, distinguished himself at the battle of Dreux, took Tancarville, and contributed in 1563 to the recapture of Havre from the English.
During the next ten years Castelnau was employed in various important missions: first to Queen Elizabeth to negotiate a peace; next to the duke of Alba, the new governor of the Netherlands. On this occasion he discovered the project formed by the Prince of Condé and Admiral Coligny to seize and carry off the royal family at Monceaux (1567). After the battle of St. Denis he was again sent to Germany to solicit aid against the Protestants; and on his return he was rewarded for his services with the post of governor of Saint-Dizier and a company of orderlies. 
At the head of his company he took part in the battles of Jarnac and Moncontour. In 1572 he was sent to England by Charles IX to allay the excitement created by the St. Bartholomew's Day Massacre, and the same year he was sent to Germany and Switzerland. Two years later he was reappointed by Henry III ambassador to Queen Elizabeth, and he remained at her court for ten years. During this period he used his influence to promote the marriage of the queen with the duke of Alençon, with a view especially to strengthen and maintain the alliance of the two countries. But Elizabeth made so many promises only to break them that at last he refused to accept them or communicate them to his government. On his return to France he found that his château of La Mauvissire had been destroyed in the civil war; and as he refused to recognize the authority of the League, the duke of Guise deprived him of the governorship of Saint-Dizier. He was thus brought almost to a state of destitution. But on the accession of Henry IV, the king, who knew his worth, and was confident that although he was a Catholic he might rely on his fidelity, gave him a command in the army, and entrusted him with various confidential missions.
Castelnau died at Joinville in 1592. His Mémoires rank very high among the original authorities for the period they cover, the eleven years between 1559 and 1570. They were written during his last embassy in England for the benefit of his son; and they possess the merits of clearness, veracity and impartiality. They were first printed in 1621; again, with additions by Le Laboreur, in 2 vols. folio, in 1659; and a third time, still further enlarged by Jean Godefroy, 3 vols. folio, in 1731. Castelnau translated into French the Latin work of Ramus, On the Manners and Customs of the Ancient Gauls. Various letters of his are preserved in the Cottonian and Harleian collections in the British Museum.
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Castelnau, Michel de". Encyclopædia Britannica. 5 (11th ed.). Cambridge University Press.
- Laboureur, Jean de, ed., Les memoires de Messire Michel de Castelnau, seigneur de Mauvissiere, vol.1 (1731)
- Petitot, ed., Mémoires de messire Michel de Castelnau: seigneur de Mauvissière at de Concressaut, baron de Jonville, comte de Beaumont, Le Roger etc., vol.33, Collection de Mémoires, Paris (1823)