It comprises the provinces of Teramo (population in 1901, 307,444), Aquila (396,629), Chieti (370,907) and Campobasso (366,571), which, under the kingdom of Naples, respectively bore the names Abruzzo Ulteriore I., Abruzzo Ulteriore II., Abruzzo Citeriore (the reference being to their distance from the capital) and Molise.
The whole of the district known in ancient times as Samnium (a part of which retains the name of Sannio, though officially designated the province of Campobasso) is occupied by an irregular mass of mountains, of much inferior height to those of Central Italy, and broken up into a number of groups, intersected by rivers, which have for the most part a very tortuous course.