The Judicatus of Cagliari (Italian: Giudicato di Cagliari) is one of the four Sardinian Judicati of the Middle Ages, kingdoms of Byzantine origins.Until the beginning of the 8th century, Sardinia was a Byzantine province, but when the Arabs conquered Sicily, communications between Constantinople and its westernmost province became very difficult.

In such a situation, a local wealthy family took the power in name of the emperor and began to transmit power inside their family.

This semi-independent kingdom controls the island until Mujāhid al-ʿĀmirī, a Spanish Muslim leader, attemptsto conquer Sardinia in 1015 and so threaten Rome and Italian Peninsula.

His attempt fails due to the intervention of the Genoese and Pisan fleets, but Sardinian political institutions are devastated and the ancient Judicatus is divided into four kingdoms, of which that of Cagliari considers itself the sole heir of the ancient unitary kingdom and of the Byzantine tradition.The Judicatus of Cagliari covers the entire south and central east portion of the island and is composed of thirteen subdivisions called curatoriae.

To its north and west lies Arborea and north and on the east laies Gallura and Logudoro.

The region of Cagliari, due to its proximity to Sicily, had long been the first landing for conquering armies and the last outpost of retreating foreigners.

First seizing the Sulcis region in the southeast, the Pisans then conquered Cagliari and rebuilt the town.

Pisa has a keen interest in Sardinia because it is a perfect base for controlling the commercial routes between Italy and North Africa.

During the period of Pisan-Genoese dominance, Cagliari remains steadfastly in the Pisan camp.