MARQ.-RÈSE, MARQUIS DE, a distinguished French engineer, was descended from a noble and ancient family, and was born in July 1714, at Angoulême. After receiving an education suitable to his birth, he entered the army at the age of eighteen, and was present at the sieges of Kehl and Philippsburg. He was next engaged in the war with Bohemia. On the conclusion of peace he turned his attention to the cultivation of those sciences upon which the military art is founded. He became a member of the Academy of Sciences in 1747, and contributed to its Memoirs several papers on fortification. He also established forges at Angoumois and Périgord, for the purpose of supplying the French navy with cannons and projectiles. During the Seven Years' War the important post of French agent in the Russian and Swedish armies was entrusted to him. In 1776 he began to publish at Paris his La Fortification Perpendiculaire, ou l'Art Défensif supérieur à l'Offensif, a large work, which was completed in eleven volumes in 1796. Meanwhile he had been charged in 1779 with the task of fortifying the Isle of Aix against the attacks of the English. The wooden fort, which he constructed on a new plan, proved efficient in spite of the prognostications of his fellow-engineers. By these efforts for the promotion of military art Montalembert brought himself into debt, and was compelled to sell his foundries to the government. But the price of them could not be obtained even after frequent applications. It is no wonder, therefore, that, aristocrat though he was, he became a supporter of the principles and practices of the French revolution. A pension, awarded to him for the loss of an eye during his services to the government, was resigned for the behoof of the state; and, like a true democrat, he divorced his wife to make room for the daughter of an apothecary. In return for such conduct he was allowed to recover his sequestered estate, and to sell it for the supply of his wants. The assignats, however, which he received as the price, fell immediately in value, and left him as poor as ever. Towards the close of his life Montalembert recommended himself to the notice of the Committee of Public Safety; and was frequently consulted by Carnot on the subject of military operations. He died of dropsy in March 1800. Besides his chief work, already mentioned, Montalembert wrote Correspondance pendant la Guerre de 1757, 3 vols., 8vo, 1777; L'Ami de l'Art Défensif, 4to, 1796; and Relation du Siège de Saint-Jean-d'Acre, 8vo, 1798.