The municipality of Castrocaro Terme e Terra del Sole was formed from the merger of two distinct administrative entities. The shared seat of the Town Hall was authorized by Royal Decree in 1925.

Terra del Sole is an ancient fortified town founded in 1564 by Cosimo I de’ Medici, Grand Duke of Tuscany (son of Giovanni dalle Bande Nere). The designer was Baldassarre Lanci from Urbino, an architect, artist, and scientist who found in the “ideal city” of Terra del Sole his architectural masterpiece. Overlooking the central Piazza d’Armi, toward which the streets of the districts converge, were the public and noble buildings, while the 38 houses that were actually built, out of the 64 planned, were constructed in two of the boroughs within the magnificent fortification. Terra del Sole, the last Tuscan stronghold before the border with the Forlì territory of the Papal States, would become a customs post, the provincial capital, the seat of the Tribunal, and the headquarters of the Grand Ducal Commissariat, which was moved here from Castrocaro in 1578. It remained in Terra del Sole until 1784, when the province was abolished.

Castrocaro, known to the Romans as Salsubium due to the notable presence of saline waters, and also referred to as Castrum Cari or Castro Cario, is mentioned by Dante Alighieri in Canto XIV of the Purgatorio. The castrum is already documented as early as the 11th century. In 1403, Pope Boniface IX sold it, together with the surrounding territory, to the Republic of Florence, for which it became the seat of military and governmental authorities. After the construction of Terra del Sole, Castrocaro’s importance declined rapidly, and the former “capital” became a rural village. The beginning of its revival, eventually leading to its prominent role among Italy’s spa resorts, dates back to 1830. In that year, the Florentine professor Antonio Targioni Tozzetti accidentally discovered that the water collected in the area known as “Cozzi” contained a significant amount of iodine and bromine, and he immediately recognized their therapeutic properties.

Terra del Sole and Castrocaro were part of the so-called Tuscan Romagna. In 1923, Benito Mussolini decided that all the Tuscan territory on this side of the Apennine ridge should once again become part of the Forlì area. In this way, he set in motion an operation intended to make the province in which he was born more important and prestigious—a province that could boast possession of the sources of the Tiber River, the sacred river of Rome. Castrocaro, strengthened by its new spa development, began to demand the transfer of the municipal seat. Terra del Sole, of course, had a different view. The new town hall was therefore built in a location equidistant between the two rival centers.

The first spa establishment in Castrocaro officially opened on June 1, 1851. However, the creation of the first nucleus of today’s spa complex required the initiative of Aristide Conti, a young nobleman who, after marketing salt, bromine-iodine-lithium compounds thanks to a patent dated May 22, 1871, went on in 1884 to build a thermal spa facility with an adjoining park. The complex was connected to the springs through a system of pipes that supplied the baths and fountains. From this initial phase, later extensively renovated, the “Tempietto delle Acque” still survives today.

Among the many distinguished guests, the Conti Baths were regularly frequented by several members of the family of Benito Mussolini. However, in light of the financial difficulties of the then “Società Terme,” as well as political issues involving some members of the Conti family, Mussolini began to consider turning the spa complex into state property and restoring it as an exclusive center for the aristocracy and upper bourgeoisie. Above all, he wanted to associate the Castrocaro spas with his own name. Financial problems, the forced removal of the Conti brothers from local Fascist Party structures, and the growing majority shareholding of the Istituto Nazionale delle Assicurazioni led the government to place the “Società delle Terme” into liquidation—at that time still owned by the Conti family (Royal Decree, Law 09/07/1936 no. 1665)—and to proceed with the nationalization of the assets comprising the Castrocaro Thermal Company. The operation was formally justified by citing the “absolute and urgent necessity to reorganize it in the public interest.” With Law no. 11 of January 4, 1937, management of the assets was therefore entrusted to the Ministry of Finance, General Directorate of State Property. At the time of nationalization, Castrocaro already possessed high-quality accommodation facilities and a splendid park covering eight hectares, rich in valuable plant species and widely praised in the press. The thermal establishment included forty bathing rooms, eighteen mud-treatment rooms, departments for inhalation and irrigation therapies, and a massage service.

The government plan promptly drawn up (1936–1937) called for the construction of three buildings considered essential to the creation of the “Thermal City”: the Bathing Establishment, the Grand Hotel, and the Pavilion of Entertainment, thus “implementing higher directives for the enhancement of that important spa resort in the land of Romagna.”

Thanks to the development of its spa facilities, Castrocaro gradually achieved a significant growth in the quality and quantity of its hospitality, commercial, and tourist offerings.

Today, thanks to substantial private investments, the Terme di Castrocaro complex is a cutting-edge center for wellness and spa treatments, an outpatient medical facility accredited by the Italian National Health Service, and a rehabilitation center.