At the time of the signing of the Convention du Mètre and the foundation of the Bureau International des Poids et Mesures (BIPM) in 1875, the Pavillon de Breteuil was already more than two hundred years old. Built by Thomas Gobert for 'Monsieur' and inaugurated by Louis XIV in 1672, it had seen the glories of Louis XIV and the turbulence of the French Revolution, had been restored and refurbished by the Emperor Napoléon and, finally, had been seriously damaged in the Franco-Prussian war of 1870. This short account of the three hundred years of the Pavillon de Breteuil is meant to complement the description of the scientific work carried out by the Bureau International des Poids et Mesures entitled Le BIPM et la Convention du Mètre.
Very little of what is presented here is the fruit of our own researches. Instead it is based upon what has been written or told to us by others. We have drawn heavily upon a history of the Pavillon de Breteuil, written some forty years ago and to the best of our knowledge never published, by Mme H. Kranz-Manoncourt. We are pleased to acknowledge the contribution of M. and Mme de Breteuil in particular for the copy of the Baron de Breteuil (now hanging in the Château de Breteuil) and of the Abbé de Breteuil and for other information on the Baron. We are also pleased to thank Mme O.A. Schmitz, in charge of the museum of the Parc de Saint-Cloud, for helpful advice and information much of which was in a brochure accompanying an exhibition on the Château and gardens of Saint-Cloud in the museum of the Domaine National de Saint-Cloud in 1989. The copy of one of the earliest plans of the present site of the Parc (from the Manufacture Nationale de Céramique de Saint-Cloud), the 'plan terrier' of the Hotel d'Aunay of 1577 (Maison de Gondi), was also kindly supplied by Mme Schmitz. We are also very grateful to M. P.-X. Hans, Inspector of Historic Monuments, for helpful advice and notes on his research into the early history of the buildings of the Parc de Saint-Cloud. From these it appears that the existing building of the Pavillon de Breteuil is indeed the original Trianon de Saint-Cloud of 1672 which was transformed in 1743 to its present form and not, as had previously been thought, a new building erected on the site of the demolished Trianon.
We hope that what we have assembled here will go some way towards answering the many questions asked by visitors to the Pavillon de Breteuil about the history of what is, by any standards, a fine and elegant building in beautiful surroundings.