What they bought most was bread as for a long time a basic element of food.
It seems that the corn which fed initially Paris is the corn of Beauce, because the oldest market, in the Ile de la Cité , was called "Beauce market". The corn arrived by the river Seine and was discharged at the "Greve" market (currently "Town Hall" square). The mills of the "Grand Pont" changed it in flour. During the reign of Philippe-Auguste, this market became too small and at this point in time the king had the "Halles" market open. The ordinance of March 12, 1322 specified the opening hours of the three markets: the "Greve", mentioned above: 6 a.m. then the "Juiverie", then the last one, the "Halles" at 9 am.
Its routing only depended very little on the water ways. The herds walked on from Maine and Perche and sometimes even from as far as Limousin and Marche. The Parisians were large-scale consumers. There were two markets: one in the "Pourceaux" square (at the junction of rue de la Ferronerie and rue des Dechargeurs (Unloaders), the second on Place aux Veaux, close to the Grande Boucherie.