Dozens of kilometers of galleries were dug in the chalk of the Drouais plateaus, to extract the marl used to amend the clay soils. From the 12th century, the troglodyte cellars of the Saint-Thibault priory had a very different destiny. 

 

For seven centuries, the Cistercian monks stored there "many vessels and casks filled with wine from Dreux", fruit of the tithe imposed by the church on the hundreds of Drouais winegrowers. 

 

Lined with Vernon limestone and pointed arches resting on Epernon sandstone corbels, these are examples of 12th century Romanesque architecture.