William I (c. 1160–1214), royal name Salusio IV, was the judike of Cagliari, meaning "King", from 1188 to his death. His descendants and those of his immediate competitors intermarried to form the backbone of the Italian Aristocracy, and ultimately their descendants in the Medici clan are precursors to, and definers of later royalty and claims thereto.
William was an infamous politician and warlord in medieval Sardinia. A member in the medieval Sardinian "Judges", he consolidated his power through both military force and political intrigue. He was a soldier, a military man, and a merchant. He assisted his father in the conquest of Cagliari, and later accompanied his Archbishop (Ubaldo Lanfranchi, Archbishop of Pisa) on the Third Crusade. He claims to have led the force defeating the Visconti in a civil war, only to later hand Pisa back to them while marrying into the Visconti family. Being closely related to many high ranking clerics, he maintained close relations with the papacy until his death. Allegedly, he was a man of some culture, as he was in reportedly in contact with the Provençal troubadours Peire de la Caravana and Peire Vidal, likely to contract their services on behalf of his wealthy patrons.
Rise to power in Cagliari
He was the son of Giorgia, daughter of Constantine II of Cagliari, and Obert, Margrave of Massa. He was a brother of William, Margrave of Massa. His paternal relatives were a branch of the Obertenghi who ruled Massa Lunense from the 11th century. Constantine II's eldest daughter married a younger son of Gonario II of Logudoro. This man, Peter, ruled the giudicato on her behalf (as Torchitorio III) following the death of Constantine. While Constantine, like the Massa, had been a vassal of the Republic of Pisa, Peter transferred his allegiance to the Republic of Genoa. In 1187, open conflict raged over the whole island of Sardinia between the Genoese and their factions and the Pisans and theirs. The Pisans mercilessly assaulted Genoese merchants in Cagliari and despoiled their landed possessions, evicting them from the giudicato. In 1188, Peter was captured and imprisoned, never to be heard of again. By 1190, William was judge in his place. Because of the interval between Peter's known arrest and William's first appearance as judge, some scholars have alleged that William's father, Obert, ruled the giudicato as judge in the intervening period, but this is unsupported by any documentary evidence and is based on arguments from silence. The period of silence may be explained by William's accompaniment on the Third Crusade with Ubaldo, Archbishop of Pisa, a pilgrimage which is referenced in a papal letter of early 1200.
William established his court at Santa Igia and took the regnal name Salusio IV, continuing a tradition of alternation between the two regnal names (Torchitorio and Salusio) and also demolishing the theory that he had had any other predecessor than Torchitorio III. On 7 July 1188, the emissaries (cardinals) of Pope Clement III declared a general peace to be observed on the island. They affirmed Pisan supremacy over Genoese estates and over the giudici. Nevertheless, in June 1191, Constantine II of Logudoro signed a treaty with Genoa. The treaty explicitly called for the maintenance of peace with William.
War with Logudoro
In 1194, William was at war with Constantine over Arborea. He invaded the Giudicato of Logudoro and occupied the frontier castle of Goceano. There he imprisoned Prunisinda, Constantine's Catalan wife, and her entourage. She died the subsequent year at Santa Igia of malnourishment and mistreatment. William received a strong reproof from Pope Innocent III for "dishonouring" Prunisinda.
In 1195, Constantine attacked Santa Igia without success. In March, Constantine induced a peace with William through Pisan mediation. A treaty was signed whereby Prunisinda was to be released and Constantine was reserved the right to pay for the return of Goceano or any castle of equal value. He then requested Pisan intervention to obtain a peace between himself and Peter I of Arborea, William's protégé. The war between the two rulers actually continued until Constantine's death in battle in December 1198. William meanwhile forced Constantine's ally, Hugh I of Arborea, Peter's co-judge, to accept terms and agree to marry Preciosa, his daughter and a relative through of Peter's through her mother.