This study addressed the historical phenomenon known as incastellamento, in the area of the current province of Viterbo, from a quantitative and geographical perspective. The time period considered was the 10th-15th century. The paper describes the documentary sources, historical maps, aerial images, past studies and archaeological sources that are available to researchers, and which have been used, in good measure, to reconstruct the fortified settlement network. Moreover, the paper explains the methodologies used to identify, store and geocode the whole dataset, which so far comes to a total of 191 fortified settlements. In conclusion, we discuss the main characteristics of the online atlas, intended as an open and interoperable platform to consult, query and retrieve information from the dataset of late-medieval fortified settlements.