This large section takes in virtually all the late Roman Diocese of Britanniae, with the notable exception of the south-western peninsula, already covered in Chapter 1. This is the easiest section of the text to follow as it is also the area covered by the Antonine Itinerary with the useful aids to identification – distances between places and a much more stable textual tradition – that source has to offer. Although there can be no question of the Cosmographer using the Itinerary (Rivet & Smith 1979, 191), both texts attest an interest in keeping road-books and maps, frequently as official or quasi-official documents (Chevallier 1976, 36). They thus have many points of contact and, in the case of the Cosmography, this is of great value to us.
The Antonine Itinerary takes the form of a series of lists of places along specified routes, generally between places of some importance, but occasionally also between places of no note whatsoever (for instance Iter X in the British section, which runs from Glannouenta, generally identified with Ravenglass in Cumbria, to Mediolano, Whitchurch in Shropshire, neither places of more than local significance, so far as is currently known). Its treatment of specific parts of the Empire is patchy; north-western and south-central Gaul or the Balkans, for instance, are barely covered. The British provinces, by contrast, are relatively fully documented. This difference in coverage shows that the listing was neither intended to be comprehensive nor that those places it names had any special status.
The distance between individual places named in the Itinerary is recorded in Roman miles. Despite some complications in the interpretation of the distances (Rodwell 1975, 76) and corruptions in the numbers (Rivet & Smith 1979, 154), most of the names listed in Britain can be identified with places known archaeologically as Romano-British settlements, from villages to cities and including military sites. Where a name in the Cosmography can be identified with one in the Itinerary this gives us a fixed point from which to work in identifying places not mentioned in the latter source.
Using the principle enunciated in the introduction, we can assume that in most of the instances where names in the Cosmography that can be identified by reference to the Antonine Itinerary are separated by a number of unidentified names, these unidentified names lie on or close to a route between the two identified names. Occasionally the unidentified names will give clues about their correct location as they may contain the name of a river or some other identifiable topographical feature. For much of the area covered by this section we can be confident about the identifications of names listed only by the Cosmographer. However, as we shall see, there are occasions where he makes a leap to or from a place whose identification is not fixed by the Antonine Itinerary, so we cannot be certain that we have followed exactly the same route as that taken by his eye.