Having crossed the Garonne and Ariège rivers and passed to the south of Toulouse, the army now had an open route to Narbonne and beyond to the Mediterranean, or the Greek Sea as it was known to the English at the time. The route would be along the axis of the Roman Via Aquitania, called the King's Highway by Baker, built in 118 bc to link the Via Domitia at Narbonne with Toulouse and Bordeaux. For the prince and his army the march to Carcassonne would be generally easy, along a flat valley with gentle hills rising on both sides. In one place the valley narrows to little more than half a mile but in other places it is several miles wide. The route of the Roman road is still in use today as the N113 and D33 roads.

The villages and small towns in the area were poorly defended, soft targets in today's parlance. It was a wealthy trading area and the most productive grain-producing area in France. In addition, some land was used for raising cattle and sheep, and near Castelnaudary a start had been made to the cultivation of woad which would one day bring wealth through the production of dyes.