For the calculations in kilometres and modern miles in what follows, the equivalents used are the commonly accepted 1,000 Roman paces = 1.48 km or 0.92 modern miles. The edition of Itinerarium Antonini Augusti consulted is that of G.Parthey and M.Pinder, Berlin, 1848. Iter XIV is on p. 233.
How accurate the Itinerary’s distances ever were, and whether/where the manuscript tradition might – perhaps – be corrupt, are problems to acknowledge rather than linger over at this stage. Iter XIV, on which Traiectus lies, starts at Caerleon (Isca Silurum) and ends at Silchester (Calleva Atrebatum), and is an alternative route (alio itinere) to the one via Gloucester. The total distance is recorded as CIII (103,000 paces or 103 Roman miles); and the separate distances given between each stopping point, satisfyingly, add up to exactly CIII. So far, so good.
The first stage of the iter, Isca Silurum (Caerleon) to Venta Silurum (Caerwent), is given as VIIII mpm or 9,000 paces – c. 13.32 km or 8.28 miles. As the crow flies, the distance between the two is 13.23 km or 8.22 miles. Is that what the Itinerary’s measurements mean, or is it just a coincidence? A coincidence, surely, since mille passus must refer to a distance walked (rather than flown), mustn’t it? [But see future blog on this.] The ‘predicted’ Roman road route between Isca and Venta is roughly along the A48, though little archaeological evidence seems to exist.¹ Following that route (and cutting out some of the wiggles), the distance would be at least 14.42 km or 8.96 miles.
There are reasons to think that the measurement of this stage, at least, of the journey ought to be fairly accurate. Firstly, the terrain is easy: along a flattish coastal plain, gently undulating but with no deep valleys, wide rivers, mountains or steep hills to negotiate. It’s therefore not too surprising that the as-the-crow-flies distance is almost exactly as recorded by the Itinerary. Secondly, at 9,000 paces it is one of the shorter stretches between stopping points on this iter (the shortest is 6,000 paces, the longest 20,000). Longer stretches can present more possible deviations and uncertainties; and there are always the unknowable variables introduced by the marching army or whoever measured the distances used by the Itinerary.
We can infer that the Itinerary was very accurate in its measurement here if:
a) it was measuring the ‘as the crow flies’ distance or
b) 1,000 paces represented c. 1.6 km/0.99 miles, instead of the commonly accepted 1.48m/0.92 miles. These revised equivalents can be used for calculating the other stages.
Not very much more can be learned from this stretch: there are certainties and uncertainties. Old Somerset, not for the first time, has wandered off the beaten track; but Traiectus may bring us back a little closer to home.
¹ “West of Crick, the road is assumed to follow the route of the modern A48 through Caerwent, though the section between Crick and Cat’s Ash is almost all purely conjectural, except where it passes through Caerwent where it is confirmed by the position of the gates. Although [the] modern A48 consists of a series of straight alignments, these may owe their origin at least in part to turnpiking. To the west of Penhow Castle, Ordnance Survey fieldworkers excavated a short section of agger but little further information was recorded about the results of the excavation”, Roman roads in Southeast Wales. Desk-based assessment, p. 17, report for Cadw by A. Sherman and E. Evans, Sept 2004.