The Philatelic and Numismatic Office participates in initiatives of PostEurop concerning the development of common themes for all postal administrations belonging to the association. The theme for 2017 is "castles". The postage stamp series produced for the occasion consists of two stamps. The 0.95 euro stamp features a facade of the papal palace in Castel Gandolfo where the Vatican Observatory telescope can be seen. The palace, built on ruins of part of the Albanum Domitiani, the country residence of the emperor Domitian, originally belonged to the Gandolfi family from which the modern day town in Latium takes its name. It became a patrimony of the Holy See under the pontificate of Clement VII. Over the centuries various works to enlarge and renovate the structure took place arriving at today’s current architecture. It was traditionally used by the popes as a place for vacation up until the beginning of the 1600s when Urban VIII made it his summer residence. Pope Francis, the only one not to have vacationed there, decided to allow public access to the building and its most exclusive rooms and places by transforming it into a museum. The 1.00 euro postage stamp depicts the Palace of the Belvedere, currently part of the Vatican Museums, built by Innocent VIII (1484-1492) and located at the far northern part of the Vatican hill. The stamp shows part of the facade with its characteristic bastions adorned with decorations of vases.