The Judicate of Arborea (; ; ) or the Kingdom of Arborea (; ; ) was one of the four independent judicates into which the island of Sardinia was divided in the Middle Ages. It occupied the central-west portion of the island, wedged between Logudoro to the north and east, Cagliari to the south and east, and the Mediterranean Sea to the west. To the northeast and beyond Logudoro was Gallura, with which Arborea had far less interaction. Arborea outlasted her neighbours, surviving well into the 15th century. At its greatest territorial extent it occupied the entire island except the cities of Alghero and Cagliari. The earliest known judicial seat was Tharros, though Oristano served as capital for most of its existence.
Origins
Sardinia was an imperial province of the Byzantine Empire until the early 9th century, when the aggressive expansion and relentless piracy of the Arabs and Berbers of North Africa left the central authorities of the Empire unable to effectively defend or consistently govern the island. The local Byzantine magistrates, entitled iudici, meaning "judges", were increasingly left to provide for their own administration and defense. Maintaining the traditional forms and patterns of the imperial bureaucracy, the island's iudicati, originally a type of administrative sub-division, gradually became autonomous states ruled by iudices. By the 10th century, the legal titles to these districts (like the provinces administered by dux ("Duke") and comes ("Count") in mainland Europe) had become hereditary or rotated amongst a few powerful clans.
The first important Giudice of Arborea was Marianus I (ruled 1060 – 1070) of the Thori family. In 1070, his successor, Orzocorre I, moved the capital from the ancient port of Tharros, which was exposed to Arab attacks, to Oristano.
Around the same time, Sardinia began to emerge from obscurity and come into the historian's view. Under the ambitious Pope Gregory VII, then leading a papal reform, Sardinia was integrated into the wider Christendom. By the infusion of Western monasticism and Pisan ecclesiastic rule, she became involved in the conflicts and commerce of Europe.
Lacon-Gunale dynasty
Under Constantine I of the Lacon dynasty, Arborea paid tribute to the papacy and sponsored Camaldolese monks in opposition to the monks of Marseille favoured by rival Cagliari. Constantine paid homage to Pisa for his petty kingdom and his successor was his brother Comita II. When Pope Innocent II divided Sardinia between the sees of Pisa and Genoa in 1133, Arborea fell to the former, but Comita, in the hope of furthering Arborean independence, allied with Genoa during the subsequent civil wars of that decade. In 1145, Comita was excommunicated by Baldwin, Archbishop of Pisa, and the Judicate of Arborea was nominally transferred to Logudoro.
Comita's son and successor, Barison II, put Arborea back on good terms with Pisa. He married into the Aragonese nobility, creating ties to Spain which culminated in Sardinia falling to the Crown of Aragon some centuries later. In 1164, Barison paid the Holy Roman Emperor Frederick Barbarossa to have him crowned King of Sardinia, but the emperor revoked that title the next year, though Barison continued to employ it. He finally left Pisa for Genoa, but his legacy was civil war. His son Peter I and grandson Hugh I finally divided the kingdom by the Treaty of Oristano (1192), but in the end Hugh's line, the House of Cervera (or Bas), succeeded in establishing themselves.
De Serra-Bas dynasty
While Peter II, son of Hugh, has been accused by historians of impoverishing his realm of glory, his son Marianus II expanded it substantially, even briefly ruling over a majority of the island. During the final decades of the 13th century, three other giudicati fell into the hands of either Pisa or Genoa or one of their great families, but Arborea remained independent.