The monastery of S. Sebastiano was founded in the hills outside Alatri (Aletrium) in the sixth century, according to textual sources including Gregory the Great. The present project represents the collaboration of a group of Italian and American scholars – archaeologists, art historians, and historians, to describe the history of the abbey from its foundation to the early modern period using structural analysis, archaeological survey, excavation, and archival research. The constructions have been divided into 10 chronological phases, most dated to the period between the 11th -15th centuries. Seven small trenches have clarified the plan of some phases. These have also yielded limited pottery finds confirming dating evidence otherwise indicated by relative chronology of the structures and typological associations.
The earliest structures on the site pertain to an aqueduct and terracing walls, though the original extent of the latter has been difficult to ascertain as they lie beneath subsequent structures. The original abbey comprised two parallel rectangular buildings separated by a courtyard, built on a rocky ridge below an abundant spring. These buildings were very tall; one had a second story, the other a monumental arcade of three arches, leading into the church (now entirely rebuilt). To the east of the church, a small triconch tomb was excavated in the tufo, reached by a flight of steps. These structures formed the nucleus of the later abbey, and even today the characteristic masonry of the sixth-century walls is visible, preserved in later additions.
Throughout the middle ages, as the cenobitic community of S. Sebastiano grew, the monastery enclosed the areas between the two original structures and expanded along the ridge, creating a compact complex of buildings with diversified spaces including a cloister, chapter room, refectory, kitchens, and other rooms. Modifications to these spaces occurred as the community was replaced by Clarisse in 1234, a precocious house of these mendicant sisters who required strict enclosure. In the mid-fifteenth century, the nuns were evicted, and noted humanist Giovanni Tortelli was charged with the maintenance of S. Sebastiano. Tortelli worked both to preserverve the monastic nature of the buildings and to convert the abbey into a Renaissance villa.
(Elizabeth Fentress, Caroline Goodson)