The term encastellation refers to the phenomenon which occurred throughout most of Western Europe during the Middle Ages, particularly from the end of the ninth until the twelfth century, which led to the birth of castles, intended both as a feudal residence and as a settlement or fortified village.

The first castles erected during the ninth century were simple fortified wooden constructions, whose sole purpose was defensive, whilst at the end of the tenth century stronger materials such as stone and brick began to be employed, in order to make them more suitable for controlling the territory. The castles built in Sardinia during the Middle Ages belong to different types and are the direct consequence of the time span during which they were built.

These fortresses are located mostly on high hills, in order to be effective in the defence of economically important roads and regions. A few of these structures were built as early as the sixth-seventh century, during the Byzantine domination and then rebuilt or renovated during the period of the Giudicati.

Finally, during the thirteenth and fourteenth century, with the arrival of the Pisan and Aragonese people, a new phase of construction began (fig. 1).

Fig. 1 - Sardinian encastellation (from F.C. CASULA 1980, table 40).

In the period from the early Middle Ages until the Aragonese conquest in 1325, two broad categories of castles can be identified: the "native castle" (built during the Giudicato period, from the IX-X century until the second half of the twelfth century; the "colonial castle" (built by the Pisan and Genoese people during the twelfth and thirteenth centuries). This classification, besides its chronological aspect, also reveals the different methods of construction of fortified sites and their relationship with settlements.

The first group of fortifications is characterised by the regularity of the masonry, but not of its plant, by being perched on inaccessible hills, by the distance from roads and by the lack of a directly associated inhabited settlement. These are, therefore, castles which may be dated to the beginning of the Medieval Age, built, sometimes on structures dating back to the Byzantine Age, by the Judges in order to assert their sovereignty over the territory.

The second group of castles was built in the thirteenth century by the Pisani, with the aim of consolidating their rule. They are generally structures with a regular plant characterised by the presence of a quadrangular keep and by the quality of the masonry, elements which suggest the existence of a pre-established project. They are perfectly distinguishable both from the "ancient" castles (up to the twelfth century), and from the later ones of the Aragonese age.

This second group includes the Castle "della Fava" of Posada, probably built in the early thirteenth century according to orders by the Giudici belonging to the Visconti family of Pisa, which tied its fate during this historical phase to the interests of Sardinia and particularly of Gallura (figs. 2-3).

Fig. 2 - The so-called Castle "della Fava" of Posada (from http://www.sardegnadigitallibrary.it/index.php?xsl=615&s=17&v=9&c=4461&id=62931).

Fig. 3 - The walls and the tower of the Castle della Fava

In Sardinia, castles have certainly played an important role in the movements of its built-up areas, particularly during the High Middle Ages, when due to external threats such as from the Arabs, the coastal settlements migrated to better protected and strengthened sites. However, Sardinia does not appear to show the system of population concentration within fortified structures which is typical of medieval Europe.

During the Giudicato period, the Sardinian territory was organised in administrative districts called "curatorie", which amounted to about fifty. The village where the curator lived was the capital of each of these districts. During the twelfth century, when the Pisani arrived, there was not a true headquarters within these boundaries, except in the cases of the capitals of the Giudicati and of the Bishop’s seats. At the end of the Middle Ages almost all districts housed a castle and these forts served as the capital, substituting their name to that of the villages where the curator used to live. This fact apparently demonstrates the role played by the forts erected by the Pisani: a new place of power represented by the castle was inserted in the curatorie, i.e. the traditional location of civil power, on which the villages often depended and which, among other things, were also required to provide men for the garrison. The geographical distribution of these villages shows that they are positioned around the castle, but not necessarily within the same curatoria (district). This implies the existence of a kind of castle-territory, within which the population is employed by the castle, but without physically being nearby.

This system organised in Sardinia by the Pisani could be interpreted as an attempt to change the organisation of residential spaces, but the Aragonese conquest of 1325 stopped the project which, in many ways, only appears to be outlined.