Under this system, the structure of the house did not have to appear on the outside, but could be hidden behind a glass wall, and the interior could be arranged in any way the architect liked. After it was patented, Le Corbusier designed a number of houses according to the system, which were all white concrete boxes. Although some of these were never built, they illustrated his basic architectural ideas which would dominate his works throughout the 1920s. He refined the idea in his 1927 book on the "Five Points of a New Architecture". This design, which called for the disassociation of the structure from the walls, and the freedom of plans and façades, became the foundation for most of his architecture over the next ten years.