The word “Byzantine” comes from the ancient name of the Greek town Byzantion, founded in the VII century B.C. on the site of the present day Istanbul in Turkey, on the Bosphorus (fig. 1).

Fig. 1 - (The Roman empire at the death of Constantine and indication of Constantinople from http://it.wikipedia.org/wiki/Costantinopoli#/media/File:Costantino_nord-limes_png.PNG).

In 324 Constantine decided to build a new city on the older one and it became the empire's new capital in 330 A.D. (fig. 2) with the name Nea Roma (New Rome), or, alternatively, Constantinople (City of Constantine).

Fig. 2 - Ideal reconstruction of the city of Constantinople, founded by Constantine I on the ancient Byzantium (from http://it.wikipedia.org/wiki/Costantinopoli#/media/File:Bizansist_touchup.jpg).

After the Western empire was separated from the Eastern one in 395, the latter extended and lasted until 1453, when it was conquered by the Ottomans.

During the reign of Justinian (527-565 - fig. 3), the Byzantines managed to steal Sardinia from the Vandals in 534.

Fig. 3 - Map of the Byzantine Empire: Areas in red before Justinian I (527); Areas in orange after his death (565), (from http://it.wikipedia.org/wiki/Giustiniano_I).

As of that date, the military command of the island was held by a dux Sardiniae with its headquarters «in the mountains where the Barbaricini were thought to live», place assumed to be Fordongianus. It exercised military functions, handled organisation and the defence efficiency of fortresses (castra) spread over the area, especially in the most exposed centres and the most important ones like Karales (Cagliari), Sulci (Sant’Antioco - fig. 4), Tharros, Forum Traiani (Fordongianus), Olbia, Turris Libisonis (Porto Torres).

Fig. 4 - Perspective and floor plan of the Antioco castrum (LA MARMORA 1997, p. 258, fig. 6).

In 687 Giustiniano II ordered, perhaps for safety reasons, that the dux be transferred to Cagliari where the praeses, official holding administrative functions, was already based. At times of particular danger, the two figures became a single official - called iudex provincae or archon - charged with handling threats. Progressively, that figure increased his autonomy until the Districts were slowly created and the Byzantine government came to an end in Sardinia.