In 1914 Denis purchased the former hospital of Saint-Germaine-en-Laye, constructed under Louis XIV in the 17th century. He renamed the building "The Priory" and Between 1915 and 1928, with the aid of the architect Auguste Perret, he decorated the building, particularly the unfinished chapel, which he filled with his own designs of frescos, stained glass, statues and furniture. In 1916 declared his intention to aim for the "supreme goal of painting, which is the large-scale decorative mural." he completed twenty murals between 1916 and his death in 1943.