This article is the result of a current investigation at the University of Valladolid concerning the transformations of the historic space of Santarém in the context of modern urban design. It analyses the processes of transformation of urban morphology of a polycentred structure, having one city centre in a high town on top of the city plain and other town centres in the lower part of town, (Alfange and Ribeira) along the banks of the river Tejo in a sequencial process of the selling-off of the convents and monasteries situated within and without the gates, in the surrounding area of the high walled town forming a double urban perimeter.
The selling-off results in the making available ground suitable for urbanisation corresponding to the ancient boundaries and the building fabric which takes-on new functions, transforming religious buildings into military quartels, houses, bull-rings, horse stables or public institutions. This factor gives significance to permencence and to the morphological changes in the process of transformation from high town to the city centre in the context of modern urban design. "It is necessary to find the meaning of permanence in the ancient city centres, inside the actual order of the city. The way to incorporate the old and the new on things constant and things changing." (Alfonso Mora, 1980)