Tadeusz Thaddeus (Kosciuszko), a Polish patriot, born near Novogrudek, Lithuania, Feb. 12, 1746, died in Solothurn, Switzerland, Oct. 15,1817. He was descended from a noble Lithuanian family, studied at the military academy of Warsaw, and was sent to the military school at Versailles to complete his studies at the expense of the state. On his return to Poland he rose to the rank of captain, but an unrequited passion for the daughter of the marshal of Lithuania induced him to leave his country, He embarked for America, where he received a commission as an officer of engineers, Oct. 18, 1776, and repaired to his post with the troops under Gates. He planned the encampment and post of the army on the range of hills called Bemis heights, near Saratoga, from which, after two well fought actions, Burgoyne found it impossible to dislodge the Americans. Kosciuszko was subsequently the principal engineer in executing the works at West Point, and became one of the adjutants of Washington, under whom he served with distinction. From Franklin he received the most marked expressions of esteem and commendation. Finally he was made a brigadier general, and was honored with the public thanks of congress, and with the badge of the Cincinnati. At the end of the war he returned to Poland, where he lived several years in retirement.

In 1789, when the Polish army was reorganized, he was appointed a major general. He fought gallantly in defence of the constitution of May 3, 1791, under Prince Poniatowski against the Russians, and particularly in the battle of Zielence (June 18, 1792), and in that of Dubienka (July 17), where with but 4,000 men he kept at bay 15,000 Russians, and finally made his retreat without great loss. When King Stanislas submitted to the second partition of Poland, Kosciuszko resigned his commission and retired to Leipsic, where he received from the national assembly the citizenship of France. He was bent, however, on another effort for Poland. A rising of his countrymen was secretly planned, and Kosciuszko elected dictator and general-in-chief. Suddenly appearing at Cracow, March 24, 1794, he issued a manifesto against the Russians, and, with a hastily collected host, armed mostly with scythes, advanced to meet the enemy. At Raclawice (April 4) he routed with 5,000 men a Russian corps almost doubly strong, and returned in triumph to Cracow. He received reenforcements from some former Polish detachments, and, committing the conduct of government affairs to a national council organized by himself, moved forward in quest of the Russian army.

His march was opposed by the king of Prussia at the head of 40,000 men, and Kosciuszko, whose force amounted to but 13,000, was defeated, June 6, 1794, at Szczekociny. Being unable to check the anarchy that existed everywhere in the land, Kosciuszko had laid down the dictatorship and now retired with his army to Warsaw, which city he defended with great success against the beleaguering Prussians and Russians. When the siege was raised, he reorganized his army, and went out to check the progress of the Russian forces under Suvaroff and Fersen, but was routed by their overwhelming numbers at Maciejowice, Oct. 10. Kosciuszko, falling covered with wounds from his horse, was captured by the Russians, and consigned to a prison in St. Petersburg. His imprisonment was rigorously continued during two years, until the death of Catharine, when the emperor Paul gave him his liberty, with many marks of esteem. The czar, on releasing his prisoner, offered him his own sword. "I have no need of a sword," said Kosciuszko; " I have no country to defend." No sooner had he crossed the Russian frontier than he sent back to the czar the patent of his pension, and every testimonial of Russian favor. Henceforth his life was passed in retirement.

In 1797 he visited the United States, where he was received with great honor and distinction, and obtained from congress a grant of land, in addition to a pension which he had received since the close of the war. Taking up his abode thereafter in France, he lived chiefly at a country place near Fontainebleau, passing his time in agricultural pursuits. In 1806 Napoleon, about to invade Poland, desired to make use of the patriot; but Kosciuszko, under parole not to fight against Russia, refused to lend himself to his purpose. When the allies approached Paris in 1814, Kosciuszko observed a Polish regiment committing acts of pillage. Rushing forward, he upbraided the officers for their conduct. " Who is he who dares to speak thus?" they exclaimed. " I am Kosciuszko," he replied. The effect of his name upon the soldiers was electric. Throwing down their arms, they prostrated themselves at his feet, and supplicated his pardon. The emperor Alexander, who, in an audience subsequently, held him long in conversation, made him the most flattering promises. Kosciuszko repaired to Vienna, but after the battle of Waterloo he was strangely neglected, and soon left the seat of the great European congress.

In 1816 he went to live in Switzerland, making his home at Solothurn, whence in the following year he sent a deed of manumission to all the serfs upon his Polish estate. His death was caused by a fall from his horse over a precipice. His remains were removed by the emperor Alexander to the cathedral church of Cracow, where they repose by the side of Poniatowski and Sobieski. Near Cracow there is a mound of earth 150 ft. high, which was raised to his memory by the people, earth being brought from every great battle field of Poland. From a fancied resemblance in shape to this tumulus, the loftiest known mountain in Australia has received the name of Mount Kosciusko.