The excavations at the impressive kitchen complex of the Château-Thierry castle (14th – 16th centuries) brought to light the hydraulic network that served it and its evolution. The history of the water techniques and of the relevant structures in the Middle Ages remains obscure and is not well documented in particular in the case of fortified seigneurial residences. The analysis of the archaeological data and of the written sources collected on this site show the setting and maintenance of a network fed with a very big well. The lead pipes protected with stone sheaths made it possible to bring water to different structures ( fishponds , fishpits , kitchen...) In the same way, the draining off of the waste water outside the walls of the site required the setting up of a fortified main sewer.