The Castello di Decima is a fortified building in Rome (Italy), in the frazione Castel di Decima.It is a structure closed by four arms, with a crenellated entrance accompanied by a tower. In the center, there is an internal courtyard with a circular fountain.Inside the castle rises the small . The building occupies a part of an early medieval fortification that stood at the tenth mile of the Via Laurentina, the Roman road which led to Lavinium (now Pratica di Mare).