Byzantine Sardinia

The Byzantine age in Sardinian history conventionally begins with the island's reconquest by Justinian I in 534. This ended the Vandal dominion of the island after about 80 years. There was still a substantial continuity with the Roman phase at this time. The invasion of Italy by the Longobards in 568, which changed the face of Italy, only resulted in a few coastal raids on Sardinia.
Administration.
The Byzantine Empire was an autocratic state, with its administration centralised around the Emperor. In addition to being the chief of the army he also had authority in the Church, often appointing the Ecumenical Patriarch. Following the Byzantine reconquest, Sardinia was part of the praetorian prefecture of Africa. The province of Sardinia was ruled by a "praeses provinciae", also known as the "iudex provinciae", based in Cagliari. A "dux" was responsible for military matters and was based at Fordongianus ("Forum Traiani"), which since Roman times had been a fortified bastion against the inhabitants of the Barbagia. These two most important offices, "iudex" and "dux", were unified in the 7th century. To allow for control of the routes that crossed the Tyrrhenian Sea, the island was also home to a squadron of the Byzantine fleet.
Units of the Byzantine field army, the "comitatenses", were based at Fordongianus. Along the border with the Barbagia region were fortresses such as those at Austis, Samugheo, Nuragus and Armungia. Soldiers of different origins (Germanic peoples, Balkan peoples, Longobards and Avars among others), called "limitanei" (border troops), were garrisoned here. Some of the island's garrison soldiers were "caballarii" (horsemen) and received in compensation for their military services land parcels to farm.
In the countryside there continued to be the great estates, but also smaller properties and common lands. The rural population consisted of both free people (the "possessors") and slaves, mostly living in villages (vici). They worked the private and community lands with hoes and nail plows, grazed livestock and fished. Extensive vineyards were cultivated but there seemed to have been few orchards.
End of Byzantine rule.
Sardinia was initially constituted as a "ducatus" (duchy) within the Exarchate of Africa. After the fall of the African Exarchate in the 7th century, caused by the Arab conquest of Carthage, the "ducatus" was directly dependent on Constantinople.
It became then an "archontate"; that is, a region with the same characteristics of a "theme" but smaller and less rich. The governors of the island originally held the rank of "hypatos" and later that of "protospatharios", before receiving the title of "patrikios" from the middle of the ninth century. At this time the relations with Byzantium, if not completely interrupted, had become intermittent, however. Due to Saracen attacks, in the 9th century Tharros was abandoned in favor of Oristano, after more than 1,800 years of human occupation while Caralis was abandoned in favor of Santa Igia; numerous other coastal centres suffered the same fate (Nora, Sulci, Bithia, Cornus, Bosa, Olbia among others.). Contacts between Sardinia and the Byzantine empire didn't cease, however, as suggested by the mention of Sardinian imperial guards in Costantine VII's work "De Caereimoniis" (956–959 AD).
The Sardinian "archon" had both military and civil functions. During the period of direct Byzantine rule, these were delegated to two different officers, the "dux" and the "praeses". The office of "archon" became the prerogative of a specific family who transmitted the title in succession from father to a son. At the beginning of the 11th century there was a single "archon" for the whole island. This situation changed over the following decades; the first unequivocal attestation of the existence in Sardinia of four separate kingdoms is in the letter of October14, 1073 that Pope Gregory VII (1073–1085) sent from Capua to Orzocco of Cagliari, Orzocco d'Arborea, Marianus of Torres and Constantine of Gallura.
During the early Giudicati era, the Judicate of Cagliari was a direct descendant of the former Archontate of Sardinia. It helped many Byzantine institutions, including the Byzantine Greek language, to survive. By the end of the century Greek had been supplanted by Medieval Latin and Sardinian.
Religion.
The Sardinian Church followed the Eastern Rite, in which baptism and confirmation were imparted together. Baptism was carried out by submersion in tanks where water came to the knees of the catechumens. Similar baptismal tanks are found in Tharros, Dolianova, Nurachi, Cornus and Fordongianus. Alongside the secular clergy operated the Basilian monks, who spread Christianity in Barbagia.
In the Byzantine period several cross-in-square churches were erected, with the four arms around a domed roof over their junction.