Decrypting the Peutinger Map

Case

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Unit of length is not changed at the provincial border, but at the start or end of a half-route: Tolosa – Aginnum

Although on the TP most routes use the mille passuum (mp, 1481 m) as the unit of length, within the Tres Galliae (Gallia Aquitania, Lugdunensis and Belgica, and Germania inferior and Superior) most routes use the leuga (2200-2500 m). The change of unit is expected near the provincial borders between the Tres Galliae and the rest of the empire. Most routes crossing these borders also have a coupling of opposite half-routes at the border, and therefore it is not possible to see whether the change of unit there is related to the crossing of the provincial border, or the switch from one to another half-route. But this distinction can be made at the route Tolosa – Aginnum (and Tolosa - Aquis Terebellicis). Analysis of this route makes clear the unit of length is not switched at the crossing of the border, but at a switch of half-route.


The boundary of the leuga area: “Lugduno, caput Galliarum, usque hic legas”

The relationship between distance values and actual distances shows that the boundary between the area where distance values are (mainly) expressed in leugae and the central European area where distance values are expressed in mp is located at or near the provincial border between the provinces of Gallia Aquitania, Lugdunensis and Belgica and Germania Superior on one side, and the provinces of Gallia Narbonensis, Alpes Poeninae and Raetia on the other.1 That the connections to the north-west of this border are expressed in leugae is confirmed by an entry on the TP near the gate symbol of Lugdunum (Lyon FR): ‘Lugduno / caput Galliarum / usque hic legas’, or ‘Lugdunum, capital of Gallia, up to here leugae’, meaning that to the left of Lugdunum the distances are shown in leugae, to the right of Lugdunum in mp.2 Unfortunately, the map does not give any further information about the boundary between the mp area and the leuga area.3

Following Miller, it is assumed that routes crossing this boundary change unit at the provincial border.4 However, this is not entirely true: the change takes place when switching from one half-route to another, which will be demonstrated below. The switch from one half-route to another is often close to the passage of the provincial border, but not always. Figure 3 illustrates the boundary across the first three sheets of the TP, followed by an overview of where routes cross this boundary.


Figure 1: TP sheet 1, 2 and partially sheet 3, with rivers and seas in blue. The course of the boundary between leuga and mp area in purple, with purple dots where a route is crossed. Numbers 1-9 correspond to the enumeration below.


The places where on the left side distances are expressed in leugae, and on the right side with mp, and where the unit is thus changed, are, from southwest to northeast:


  1. Tolosa (grid 1B1)5

  2. Fines (route Tolosa – Divona, grid 1B2)6

  3. Loteua (grid 1B3)7

  4. Lugduno (grid 1B5)8

  5. Gennaua (grid 2B1)9

  6. Lacum Losonne (grid 2B2)10

  7. Viromagus (grid 2B2)11

  8. Ad Fines (Halfway Vindonissa and Arbor Felix, grid 2A5)12

  9. Grinarione – Clarenna (grid 3A1)13


As indicated, routes are composed of half-routes, which are linked at or near the border between the two areas around the respective starting points of the two half-routes. It is therefore not surprising that on the said routes, the coupling will be at or near the provincial border. Whether the unit is switched exactly at the provincial border, or at the nearby coupling of half-routes, is often difficult to discern, partly because the position of the borders is only roughly known.


Figure 2: Environs of Tolosa (Toulouse FR). Although on the TP Aginnum is to the right of Tolosa, in reality Agen (Aginnum) is to the (north)west of Toulouse. Large dots indicate places on the TP with a gate symbol, small dots indicate places listed on the TP with only the name along a red line.



An exception is the situation around Tolosa (Toulouse FR), where it can be seen that the change of length unit does not take place at the provincial border, but at the end or at the beginning of the half-routes. On the TP, Tolosa is connected to four routes: to Narbone (Narbonne), Diuona (Cahors), Aginnum (Agen), and to a place which stood on the vanished left part, probably Aquis Terebellicis (Dax) (Fig. 2). Tolosa is located in the province of Gallia Narbonensis. The same applies to Narbone, and the route between the two places is therefore entirely in mp. However, the other three endpoints are in Aquitania, and the three routes there thus cross the provincial border that is associated with the boundary between the mp area and the leuga area. The use of length units on the road to Diuona is as expected: the place name ‘Fines’ located between the two regional centres will both indicate the provincial border and be the place where the two half-routes are linked. Tolosa – Fines is expressed in mp, the values between Fines and Diuona are expressed in leugae. However, analysis shows that this is very different on the other two routes that start in Tolosa.


Case Tolosa – Aginnum (grid 1B1-1B2)


Figure 3: Tolosa (Toulouse FR) - Aginnum (Agen FR). No distance value is given between Lactora and Aginnum.


This route initially connects Tolosa (Toulouse FR), capital of the Volcae Tectosages, with Lactora (Lectoure FR), capital of the Lactorates: Tolosa – 20 – Sarnali – 16 – Lactora – ? – Aginnum (see Fig. 3).14 The border between the two civitates is expected at Sarnali, which is associated with Sarrant FR. The last connection of the route, Lactora – Aginnum, has no distance value. This indicates that the route was based only on a half-route from Tolosa towards Aginnum, which ended in Lactora.15 Unfortunately, the creator of the TP did not have a half-route available from Aginnum towards Tolosa, which could have completed the route's information. This route is therefore of type E (see article 2, Section 'Half-routes').


The half-route Tolosa – Lactora, consisting of two connections, thus runs partly through the province of Gallia Narbonensis (where the use of the mp can be expected), partly through the province of Aquitania (where the use of the leuga can be expected). Yet both links are expressed in leugae, indicating that the location of the provincial border is not decisive here; had the actual location of the provincial border been decisive for the choice of unit, Tolosa – Sarnali would have been expressed in mp.16 The half-route is therefore decisive for the choice of unit: within a half-route there is no change of unit, but the same length unit is used for all connections. The same applies to the route between Tolosa and Aquis Terebellicis, which unfortunately has not been fully preserved. On this route, Elusa (Eauze FR) seems to be the place where two half-routes are linked, partly because at Elusa the route clearly changes direction. Here, the provincial border is expected near Casinomago, and had this border been decisive, Tolosa – Casinomago would have been expressed in mp; however, also on the half-route Tolosa – Elusa, all distance values are expressed in leugae.17 The Itinerarium Burdigalense, which similarly follows the route Elusa – Tolosa – Narbone, also uses the leuga up to Tolosa, after which it switches to mp.


1Actual distances are determined using Google Maps, ‘pedestrian’ setting. The quotient of the actual distance and the stated distance value gives the approximate size of the unit of length.

2A similar sentence is found with Ammianus Marcellinus (Res Gestae 15.11.18), speaking of the Rhone near Lyon: “... qui locus exordium est Galliarum. Exindeque non millenis passibus sed leugis itinera metiuntur.": ”... which is the place of the beginning of Gaul, and from there the journeys are not measured in mp, but in leugae.” Miller 1916, 81.

3Talbert 2010, 115 and note 192: Talbert also states that this notice is of little use to any traveller consulting this map, and assumes it is a later addition. The similarity with the entry to Ammianus Marcellinus suggests that the notice ‘till here leugae’ was added (by a later user) after consulting this or a similar text.

4Miller 1916, XLIX: “Die Grenzen fur diese Maßeinheit fallen mit den Provinzgrenzen zusammen.”

5The connection from Tolosa to Casinomago and beyond, and the connections from Tolosa towards Aginnum are in leugae, but the connection to Fines towards Diuona and the connections towards Narbone are expressed in mp. The TP seems to give the name ‘Bibona’; however, other sources suggest that ‘Diuona’ should be read here. On the TP, the capital letters B and D are barely distinguishable from each other. Rigal 2009. That the start of the latter route is expressed in mp is not 100% certain, by the way, since the locations of Badira and Fines are not confirmed by any other source and the connection between Fines and Eburomagi has no distance value.

6Towards Tolosa in mp, towards Diuona in leugae. Miller 1916, 96-97.

7Towards Segodum in leugae, to Cesserone in mp. Miller assumes that Condatomagus – Loteva is also expressed in mp instead of leugae. He therefore arrives at too small a total distance, and introduces an additional connection of 12 mp. Miller 1916, 122.

8To Furo Segustavarv{m}, towards Cabillione, and also to Mediolano (which is erroneously linked not to Lugdunum but to Furo) in leugae, but to Vigenna in mp. Miller 1916, 81-82.

9Towards Vigenna in mp, to Lacum Losonne (towards Augusta Pretoria) in leugae. Miller 1916, 124.

10Distance values from Lacum Losonne towards Vesontine and to Gennaua (towards Vigenna) are in leugae; towards Vivisco and Augusta Pretoria in mp. Miller 1916, 73-74.

11Towards Auenticum Heletiorum in leugae, to Vivisco in mp. Miller 1916, 126.

12Distance values from Vindonissa towards Augusta Ruracum and towards Samulocenis are in leugae; no distance value is given between Vindonissa and Ad Fines. Between Ad Fines and Arbor Felix the value is in mp. Miller questioned the unit used between Ad Fines and Arbor Felix: Miller 1916, XLIX, and 57. He assumes the association Ad Fines = Pfyn. According to the Barrington Atlas, the route Arbon (Arbor Felix) – Windisch (Vindonissa) runs from Arbon westwards, crosses the river Thur 3 km east of Bussnang to the left (southern) bank, to cross back to the right bank at Bussnang, eventually arriving in Pfyn; on the way to Windisch the Thur is crossed again. A shorter route is to cross the Thur from Arbon at Bussnang and continue directly to Windisch, thus crossing the Thur only once. In that case, the Thur is the natural border between the areas of Arbor Felix and Vindonissa, and the Roman bridge over the Thur at Bussnang is the ‘Fines’ (border place) listed on the TP between the two places. Comparison of the distance value with the actual distance then shows that the unit of length used is the mp.

13No distance value is given between these two places. Samulocenis – Grinarione is expressed in leugae, the stretch from Clarenna to Regino in mp. Miller 1916, XLIX, and 261, 264. According to Miller, Clarenna – Ad Lunam was possibly also expressed in leugae, but there was also no clarity yet about the location of Clarenna. He mentions Kirchheim unter Teck and Weilheim as possible locations for Clarenna, both reasonably close to Köngen (Grinarione) and at a distance from Ad Lunam; today Clarenna is associated with Donnstetten, which is more in line with a distance value in mp.

14The beginning of this name is heavily damaged. Various spellings have been proposed in the past: Sarali, Sarrali, Sartali. Miller sticks to Sa[...]ali. Nowadays, the spelling Sarnali is customary.

15See the subsection on ‘Half-routes’ and Raas 2025.

16Roth 1860, 11.

17Again, Miller pays no attention to the fact that the use of units of length here deviates from his premise that the location of the provincial border is decisive: Miller 1916, 122.

Bibliography

Miller, K. 1916. Römische Reisewege an der Hand der Tabula Peutingeriana. Stuttgart: Strecker und Schröder.

Raas, E. 2025. “Decrypting the Peutinger Map: The ‘half-route’ solution to the incorrect distance values on the Tabula Peutingeriana, and the source material for Roman itineraries” In: Orbis Terrarum 23, edited by M. Rathmann. Stuttgart: Franz Steiner Verlag.

Rigal, D. 2009. “Un regard nouveau sur Cahors-Divona, chef-lieu de la cité des Cadurques”, in Pallas, no 79, 377-399. DOI: 10.4000/pallas.15517

Roth, K.L., 1860. “Geschichte der leuga”, In: Jahrbücher des Vereins von Alterthumsfreunden im Rheinlande Bd. 29/30, 1-20.

Talbert R.J.A. 2010. Rome’s World: the Peutinger Map Reconsidered. Cambridge: Cambridge University Press.

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