The six excavation campaigns on the fortified site of Col di Castiel have to date uncovered more than half of the area within the curtain wall. The excavations are part of the “Alta Valle del Tagliamento” project in Carnia, begun in 2004 by the Department of Medieval Archaeology, Faculty of Humanities at Ca’Foscari University, Venice, under the direction of Prof. Sauro Gelichi.

The curtain wall surrounded the hilltop, running along the entire eastern edge and gradually sloping down along the west side of the hill, along the line of the present footpath. The area enclosed by the fortifications was relatively small and characterised by the presence of a series of small towers along the curtain wall (two have been identified to date), which represent the archaeological contexts with the largest occupation deposits. What appeared to be a third tower was instead revealed to be the fortified structure of the castrum entrance, situated in the south-western corner of the site, where the external curtain wall runs parallel to an inner wall for about 20 m, creating a sort of obligatory passageway leading to the summit.

The stratigraphy was generally shallow. Most occupation evidence came from inside the towers, along the terrace present on the south-western hill slope in the recently excavated entrance area. Traces of a fire were found in each of these contexts, constituted by a thick layer of charcoal within which the largest number of finds were preserved. The study of the pottery, glass and metal finds indicated that the site was occupied between the 4th and 5th century A.D.

The structural characteristics and the archaeological levels suggested that a small number of people occupied the site. The most reliable theory is that this was a defensive garrison, used by a high- ranking individual for the purpose of levying taxes or tolls for the transit of people and goods.