HESSE-DARMSTADT, a grand-duchy in Germany, the history of which begins with the partition of Hesse in 1567. George I. (1547-1597), the youngest son of the landgrave Philip, received the upper county of Katzenelnbogen, and, selecting Darmstadt as his residence, became the founder of the Hesse-Darmstadt line. Additions to the landgraviate were made both in the reigns of George and of his son and successor, Louis V. (1577-1626), but in 1622 Hesse-Homburg was cut off to form an apanage for George's youngest son, Frederick (d. 1638). Although Louis V., who founded the university of Giessen in 1607, was a Lutheran, he and his son, George II. (1605-1661), sided with the imperialists in the Thirty Years' War, during which Hesse-Darmstadt suffered very severely from the ravages of the Swedes. In this struggle Hesse-Cassel took the other side, and the rivalry between the two landgraviates was increased by a dispute over Hesse-Marburg, the ruling family of which had become extinct in 1604. This quarrel was interwoven with the general thread of the Thirty Years' War, and was not finally settled until 1648, when the disputed territory was divided between the two claimants. Louis VI. (d. 1678), a careful and patriotic prince, followed the policy of the three previous landgraves, but the anxiety of his son, Ernest Louis (d. 1739), to emulate the French court under Louis XIV. led his country into debt. Under Ernest Louis and his son and successor, Louis VIII. (d. 1768), another dispute occurred between Darmstadt and Cassel; this time it was over the succession to the county of Hanau, which was eventually divided, Hesse-Darmstadt receiving Lichtenberg. During the 18th century the War of the Austrian Succession and the Seven Years' War dealt heavy blows at the prosperity of the landgraviate, which was always loyal to the house of Austria. Louis IX. (1719-1790), who served in the Prussian army under Frederick the Great, is chiefly famous as the husband of Caroline (1721-1774), "the great landgravine," who counted Goethe, Herder and Grimm among her friends and was described by Frederick the Great as _femina sexu, ingenio vir_. In April 1790, just after the outbreak of the French Revolution, Louis X. (1753-1830), an educated prince who shared the tastes and friendships of his mother, Caroline, became landgrave. In 1792 he joined the allies against France, but in 1799 he was compelled to sign a treaty of neutrality. In 1803, having formally surrendered the part of Hesse on the left bank of the Rhine which had been taken from him in the early days of the Revolution, Louis received in return a much larger district which had formerly belonged to the duchy of Westphalia, the electorate of Mainz and the bishopric of Worms. In 1806, being a member of the confederation of the Rhine, he took the title of Louis I., grand-duke of Hesse; he supported Napoleon with troops from 1805 to 1813, but after the battle of Leipzig he joined the allies.