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, and attempted to bring about a reconciliation between Mary and Queen Elizabeth. The wise and moderate counsels which he offered to the former were unheeded. In 1562, in 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 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 massacre of St Bartholomew, 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 Mauvissière 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 Laboureur, 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.
His grandson, Jacques de Castelnau (1620-1658), distinguished himself in the war against Austria and Spain during the ministries of Richelieu and Mazarin, and died marshal of France.
See Hubault, Ambassade de Castelnau en Angleterre (1856); Relations politiques de la France ... avec l’Écosse au seizième siècle, edited by J.B.A.T. Teulet (1862); and De la Ferrière, Les Projets de mariage d’Elisabeth (1883).
CASTELNAUDARY, a town of south-western France, capital of an arrondissement in the department of Aude, 22 m. W.N.W. of Carcassonne, on the Southern railway between that city and Toulouse. Pop. (1906) 6650. It is finely situated on an elevation in the midst of a fertile and well-cultivated plain; and its commercial facilities are greatly increased by the Canal du Midi, which widens out, as it passes the town, into an extensive basin surrounded with wharves and warehouses for the timber used in the upkeep of the canal. The principal buildings are the law court, the hôtel de ville, and the church of St Michel, dating from the 14th century; none of these offers any feature of unusual interest. There are a number of flour-mills, as well as manufactories of earthenware, tiles and blankets; an extensive trade is maintained in lime, gypsum, timber, grain, fruits, wine, wool, cattle and farm implements, and the building of canal boats forms an important industry. The public institutions include the sub-prefecture, tribunals of first instance and of commerce, a communal college and a farm school.
Castelnaudary probably represents the ancient town of Sostomagus, taken during the 5th century by the Visigoths, who, it is conjectured, rebuilt the town, calling it Castrum Novum Arianorum, whence the present name. Early in the 13th century the town was the scene of several struggles during the war against the Albigenses, between Simon IV., count of Montfort, and Raymond VI., count of Toulouse, and their supporters. In 1229 it was deprived of its ramparts, and after these had been rebuilt, it was captured and burned by the Black Prince in 1355, but again rebuilt in 1366. In 1632 it was the scene of a cavalry engagement in which the rebel Henry II., duke of Montmorency, was defeated and captured by the royal troops.
CASTELSARRASIN, a town of south-western France, capital of an arrondissement in the department of Tarn-et-Garonne, 12 m. W. of Montauban on the Southern railway. Pop. (1906) town, 3189; commune, 7496. Castelsarrasin, situated on the left bank of the lateral canal of the Garonne and about a mile from the right bank of that river, is surrounded by promenades occupying the site of the old fortifications. Its chief building is the brick-built church of St Sauveur, which dates from the 13th century. The administrative buildings are modern. The town has a sub-prefecture, a tribunal of first instance, and a communal college. The principal industrial establishment is the metal-foundry of Sainte-Marguerite, where copper, tin and other metals are worked; there are also flour-mills, saw-mills and dye-works. Trade is in cattle, agricultural produce, wine, baskets and game.