The route from Boulogne (Bononia gaulish "low place" as opposed to Gesoriacum gaulish gaesum "spear" with acum "place", the citadel on its rocky spur) leaves the town on the right bank of the Liane (Elna celt. Helina with river suffix on "the marshy"). It continues with short straight sections through Isques (Isecca 1069, ger. masculine name Iso with acum), Hesdin L'Abbé to Samer (Sanctus Ulmarus lat. sanctus and ger. masculine name Wulfmar).

Turning south, a single alignment leads through Panehem to the escarpment climbing it with a short easterly alignment. Just before the branch road to Hubersent (Helbess|em 1199, ger. Heldbod with ger. haim "home farm") a left turn starts a series of short straight stretches. The N1 leaves the road shortly after the branch road to Inxent (Aines|hem 12c, ger. Agin with haim). From here to Estrées (Stratae - lat. "the roman road") on the Course the line is unclear.

A field track leads from Estrée on the left bank of the Course over the high ground to the south-west. Short zigzags are used on the steepest stretch before le Vert Bois farm. In the valley on the left is the farm of Vitrouval. From here, the road follows the spur dropping abruptly to the valley of the Canche at Marles (marila - ger. "meres or ponds", the Canche (Quantia, celt. "brilliant") still crosses a marsh here.

The opposite spur at le But de Marles carries the road to Therouanne, marked on the spur by a boundary, but visible as a straight metal track leading to the north-east from the highest point of the modern road. Boundaries follow the road across the valley to Brimeux (Briva|magos - Gaulish "crossing|field") on the left bank of the Canche in the country of the Ambiani.

From here the road climbs in a straight line to the 80 m spot height at the junction with the D 130. A kink eastwards avoids the scarp slope at St Remy au Bois but the line is unclear to the Authie (Alteia) at Dommartin (Domnus Martnius 1105). A bridge at Ponches - Estruval (Pontius - Stroom|val lat. "bridge" and ger. "river valley") carried the road across the river.

A steep climb past the Chateau de Dompierre (Domnus|Petrus) on the left brings the road onto the high plateau between the Authie and the Somme. Passing Ligescourt (Luitgis|cortis, ger. masculine name Luitgis with lat cohortis "farmyard") and Wadicourt on the left, the road continues absolutely straight to Estrées-lès-Crécy (Stratae - lat. "the Roman road"). Leaving the Crécy (Crisci|acum 660 gal. masculine name Crixos with acum) battlefield and the source of the Maye on the right, the road (the D 108), passes Bezencourt and Belinval to reach Brailly-Cornehotte (Bragius|acum) and Noyelles en Chaussée (Niga|villare, lat. "the new farm or village").

This new settlement may have taken land from Yvrench (Wiberentium 830) whose territory is bisected by the Roman road. Settlement boundaries that align with the road were obviously drawn after the road was built. Territories bisected by the road may predate its construction.

The road then climbs to 114 metres before crossing the valley holding Hanchy, the railway and the road to Coulonvillers ( Coloni|villare, lat. "farm of the veterans"). After its high point of 118 metres the line descends to Domqueur (gaulish Duro|corio "fort|army", or Duroco|regum "gateway|royal").

From Domqueur the road passes the intrusive Flemish settlement of Gorenfloss (1114) on the right and continues to the track on the right to Brucamps (Brun ger. masculine name with lat. campos "fields"). Here a thirty degree turn to the left avoids the 116 metre spot height behind Surcamps. Turning to the right a new line, almost parallel to the original, takes the road down to the Niévre at St Ouen.

Leaving St Ouen the road takes a more south easterly alignment as a forest path to St Vaast en Chausée. Here it becomes the D12 and continues direct to Amiens (Samaro|briva Ambianis, gaulish "calm", the name of the Somme, with gaulish briva "bridge, crossing" and the tribal name Ambiana).