Based on an idea imagined by Philibert Delorme in the 16th century, the architect Henri Deneux undertook to rebuild the framework of Reims Cathedral. He used his principle of easily transportable pieces keyed together but applied it to concrete instead of wood. Deneux's method, at first controversial, allowed the manufacturing and assembling of the framework's 18,000 pieces in only two years, from 1924 to 1926. Reims Cathedral was listed as a UNESCO World Heritage Site in 1991.