Under Byzantine rule, the island was divided into districts called mereíai (μερείαι) in Byzantine Greek, which were governed by a judge residing in Caralis and garrisoned by an army stationed in Forum Traiani (today Fordongianus) under the command of a dux. During this time, Christianity took deeper root on the island, supplanting the Paganism which had survived into the early Middle Ages in the culturally conservative hinterlands. Along with lay Christianity, the followers of monastic figures such as Basil of Caesarea became established in Sardinia. While Christianity penetrated the majority of the population, the region of Barbagia remained largely pagan and, probably, partially non-Latin speaking. They re-established a short-lived independent domain with Sardinian-heathen lay and religious traditions, one of its kings being Hospito. Pope Gregory I wrote a letter to Hospito defining him "Dux Barbaricinorum" and, being Christian, the leader and best of his people. In this unique letter about Hospito, the Pope prompts him to convert his people who "living all like irrational animals, ignore the true God and worship wood and stone" (). The dates and circumstances of the end of Byzantine rule in Sardinia are not known. Direct central control was maintained at least through c. 650, after which local legates were empowered in the face of the rebellion of Gregory the Patrician, Exarch of Africa and the first invasion of the Muslim conquest of the Maghreb. There is some evidence that senior Byzantine administration in the Exarchate of Africa retreated to Caralis following the final fall of Carthage to the Arabs in 697. The loss of imperial control in Africa led to escalating raids by Arabs on the island, the first of which is documented in 703, forcing increased military self-reliance in the province. Elsewhere in the central Mediterranean, the Aghlabids conquered the island of Malta in 870. They also attacked or raided Sardinia and Corsica. Some modern references state that Sardinia came under Aghlabid control around 810 or after the beginning of the conquest of Sicily in 827. Historian Corrado Zedda argues that the island hosted a Muslim presence during the Aghlabid period, possibly a limited foothold along the coasts that forcibly coexisted with the local Byzantine government. Historian Alex Metcalfe argues that the available evidence for any Muslim occupation or colonisation of the island during this period is limited and inconclusive, and that Muslim attacks were limited to raids. Communication with the central government