Ferdinand IV., king of Naples (afterward king of the Two Sicilies as Ferdinand I.), born in Naples, Jan. 12, 1751, died there, Jan. 4, 1825. When in 1759 his father, King Charles, became king of Spain, he succeeded him upon the throne of Naples, in accordance with the recent treaties of Utrecht, Madrid, and Vienna, which prohibited the reunion of the two crowns in any one prince of the house of Bourbon. Ferdinand being only eight years old, Marquis Tanucci was appointed regent. In 1768 he married Carolina Maria, daughter of the empress Maria Theresa, and left the affairs of government to his imperious wife and her favorite minister Acton. The cabinet of Madrid lost all influence over the court of Naples, which closely allied itself with the cabinets 4/ of Vienna and London, and joined the first coalition against France. Though forced in 1796 to make peace with France, Ferdinand renewed the war after the departure of Napoleon to Egypt. Austria, Sardinia, Tuscany, and Naples formed a league, and Ferdinand hurried to occupy Rome (November, 1798); but not receiving much aid from his allies, he withdrew before the arms of the French, who in 1799 entered Naples soon after Ferdinand with his family had escaped in an English fleet to Palermo. The Parthenopean republic was established in Naples, but after a few months Ferdinand was restored to his capital by a Calabrian army under Cardinal Ruffo. A terrible inquisition now began against the republicans the city was abandoned to the lazzaroni, and Ferdinand seemed to have returned only to shed the blood of his subjects.

The successes of the French in Germany and Italy obliged him in 1801 to sign a treaty surrendering a portion of his territory, and to support French troops in the remainder, thus putting Naples under the domination of France. War breaking out in 1805 between France and Austria, Queen Caroline thought it a favorable opportunity for throwing off the French yoke, and prompted Ferdinand to violate the treaty and to receive the support of an Anglo-Russian army. Hardly had he done this when Austria, conquered at Austerlitz, assented to the treaty of Presburg. Before its conclusion Napoleon sent an army against Naples, which obliged Ferdinand and his queen again to take refuge in Sicily, refused offers of negotiation, and on Dec. 25, 1805, declared that the house of Bourbon had ceased to reign over that kingdom, and gave the throne first to his brother Joseph, and in 1808 to his brother-in-law Mu-rat. Ferdinand, protected by England, was able to save Sicily from French conquest; but the queen, as little willing to bear English as French supremacy, embroiled herself with the English ambassador, Lord William Bentinck, was obliged to leave the island in 1811, and died in Vienna in 1814. Ferdinand was in 1812 forced to proclaim a constitution, and finally to resign his government to his son Francis. After Murat was dethroned by Austria in 1815, Ferdinand was restored to his former throne, and on Dec. 12, 1816, united Sicily and Naples into a single state, under the title of the Two Sicilies. He abolished the constitution which he had granted while in Sicily, but was forced to proclaim the democratic Spanish constitution of 1812 by a rising of the carbonari in 1820. He was soon after reestablished in absolute power by the Austrians.