[3] The Orsini are part of the Black nobility who were Roman aristocratic families who supported the Popes in the governance of the Papal States.

The Orsini carried on a political feud with the Colonna family for centuries in Rome,[4] until it was stopped by Papal Bull in 1511.

One of the first great nepotist popes, he made two of his nephews cardinals and allowed his cousin Giovanni Gaetano (Giangaetano, died 1232) to buy the fiefs of Vicovaro, Licenza, Roccagiovine and Nettuno, which formed the nucleus of the future territorial power of the family.

Matteo Rosso, called the Great, was the effective lord of Rome from 1241, when he defeated the Imperial troops, until 1243, holding the title of Senator.

Bertoldo's son, Gentile II (1250–1318), was two times Senator of Rome, podestà of Viterbo and, from 1314, Gran Giustiziere ("Great Justicer") of the Kingdom of Naples.

His son Romano (1268–1327), called Romanello, was Royal Vicar of Rome in 1326, and inherited the countship of Soana through his marriage with Anastasia de Montfort, Countess of Nola.

Roberto (1295–1345), Gentile II's grandson, married Sibilla del Balzo, daughter of the Great Senechal of the Kingdom of Naples.

His second son, Raimondello Orsini del Balzo, supported Charles III' coup d'état in Naples against Queen Joan I.

Relationships with the royal family remained cold under Joan II; However, when Raimondello's son Giannantonio (1386–1453) sent his troops to help her against the usurpation attempt of James of Bourbon, he received in exchange the Principality of Taranto.

This line was initiated by Guido Orsini, second son of Romano, who inherited the county of Soana, on the western side of Lake Bolsena in southern Tuscany.

[6] He and his descendants ruled over the fiefs of Soana, Pitigliano and Nola, but in the early 15th century wars against the Republic of Siena and the Colonnas caused the loss of several territories.

Two of Ludovico's daughters married relevant figures: Geronima to Pier Luigi Farnese, illegitimate son of Pope Paul III and Marzia to Gian Giacomo Medici of Marignano, an important general of the Spanish army.

Thanks to the strategic positions of their fiefs, and to their famous castle built in Bracciano in 1426, they were the most powerful Orsini line in the Lazio.

The son of Girolamo Orsini and Francesca Sforza, he was grandson, on his father's side, of Felice della Rovere[7] (illegitimate daughter of Pope Julius II) and Gian Giordano Orsini and, on his mother's side, of Count Bosio Sforza and Costanza Farnese, an illegitimate daughter of Pope Paul III.

He was succeeded by Virginio, whose heir Paolo Giordano II married the princess of Piombino and was created Prince of the Holy Roman Empire.

This, along with a general economical decadence, damaged the dukedom, and last Duke and Prince, Flavio (March 4, 1620 – April 5, 1698) was forced by the huge debts to sell it to Livio Odescalchi.

Most of his fief was located in northern Lazio, but he entered in the Neapolitan orbit when in 1418 he was called by Sergianni Caracciolo to fight against the Angevine troops, which he defeated.

He was made Duke of Gravina by King Alfonso, a title definitely assigned to his son Giacomo (died 1472), to which had been added the counties of Conversano, Campagna and Copertino.

After the heirless death of Duke Michele Antonio (January 26, 1627), his lands passed to his cousin Pietro Orsini, count of Muro Lucano (died 1641).

The latter's nephew Pier Francesco, who had renounced the succession in favour of his brother Domenico to become a Dominican, was later elected pope with the name of Benedict XIII.

This branch of the family moved to Rome in the 18th century, where Duke Domenico (November 23, 1790 – April 28, 1874), married Maria Luisa Torlonia in 1823.

L'Idole (R. Merle) also has Paolo and Lodovico Orsini as main protagonists, since the book is about Vittoria Accoramboni's life.