Jouars-Pontchartrain (French pronunciation: [ʒwaʁ pɔ̃ʃaʁtʁɛ̃] ⓘ) is a commune in the Yvelines department in the Île-de-France region in north-central France.

Its territory is irrigated by the Mauldre whose south-north oriented course follows the eastern limit of the town and receives in the park of the Château de Pontchartrain the Élancourt brook, a diversion of which feeds its pond.

The farm of the Ithe, located on the banks of the Mauldre and to the west of the hamlet of Jouars corresponds to an ancient Gallo-Roman settlement called Diodurum or Divo durum, one of the largest secondary settlements recorded in Île-de-France.

The settlement developed in the valley of La Mauldre, at the crossroads of several roads leading to other Gallo-Roman settlements: Le Vieil-Évreux, Dreux, Chartres, Orléans, Sens, Paris, Beauvais.

As a large crossroad located on the borders of the territory of the Carnutes, near Belgian Gaul and possessing pre-urban characteristics, this vicus is one of the assumptions[7] for the consecrated place of the druids assembly mentioned by Caesar.