The monastery of Holy Trinity of Cava, near Salerno, founded around 1025, became the heart of a vast confraternity which extended over a great part of the Southern Italy between the XI and the XII century. Born under the direct protection of the princes of Salerno, even after their defeat, the Trinity mantained a preferential relationship with the influential ranks of the political system (formerly with the dukes of Apulia, later with the kings of Sicily). Nevertheless, the Trinity was never a direct expression of such powers, but was able to benefit from the political change in a seigneurial way, a transformation that occurred in the Southern Italy in those years. The aim of this research is to analyse, on a regional basis, the relationship of the monastery with the main territorial powers and with the rural areas as well, in order to highlight some of the monastic strategies of power achievement and, on the other hand, underline the close relationship between the different local societies and general political events. In this reconstruction, based mainly on unpublished sources, the image of a complex transformation which involved all levels of society, in the gradual change from an ancient regional and overregional political order, to a new seigneurial order, which advanced in a few years emerge. The growth of Cava, as those of many others monastic congregations of southern Italy, was at the same time a consequence and an essential part of those changes.