The idea to adapt the Palace of the Dukes to National Palace, with a museum that could be visited, was never officially expressed.  There were disagreements between the Portuguese politicians, the chief executives and the architects from the Directorate General for Buildings and National Monuments, with regard to the use to be given to the building.  The latter intended the Palace to shelter a small museum, but the Minister of Public Works, Arantes de Oliveira, preferred to give it a political function.  This minister provides indication for the rooms on both sides of the Chapel to be aimed at receiving two Chiefs of State, whereby, half of the building would have an exclusively residential function.

The other part, or rather, the remainder of the building, was handed to the Furniture Commission, while its architectural restoration was concluded, for the definition of the use of the rooms that remained of the Palace, more specifically, the entire ground floor and the Palace’s auditorium, the 1st floor.  That commission would be the one responsible for the conception of the remaining monument as noble manor that could be visited, in order to meet with the main criteria of establishing a presidential residence and one for the reception of guests of honour.

This decorative conception tried to reconstitute “how life would have been inside the Palace at the end of the Middle Ages, deduced from the building’s blueprint and from its interior items”.  Names would be created for each room, which would be maintained as museum criterion, based on the interpretation that the details that the Furniture Commission spun about the primitive dynamics and articulation of the areas.

However, this commission makes it clear that it could not manage an “integral reconstitution, rooted only on the era of its first owners because the building will now be called upon to perform functions that allow it to be used”.  Therefore, the two reasons for not adopting exclusively medieval furniture and decoration were, the practical impossibility of obtaining exclusively medieval furniture effects in such a short time and for an acceptable financial cost, and also, to respect this work’s nationalist nature.

In accordance with this reconstructive criterion, the replica was assumed as the most accessible resource to obtain items of furniture in the least onerous way.  It was actually considered that the replicas had the same artistic merit and documentary value, from the point of view that they served as “history lessons”.  The practical use of the restored monument conferred moral and justificatory validity to restoration.

The architect, Luís Benavente, director of the Service of Monuments of the DGEMN between 1952 and 1959, said that “such a Palace does not have to be prepared only to be seen, but to be lived” and that “the conclusion of the works compels such an important building to be used, which depreciation would be immediate and consequent from its lack of purpose, or from its closure”.

By order of the President of the Council, Dr. António de Oliveira Salazar, published in Decree-Law 42.365, dated 4 July, 1959, the Palace of the Dukes is to be treated as a National Palace.  In 1959, on 26 August, it is opened to the public for the first time, as Museum, having received about 200 visitors on that day.