One of the largest in Spain, the Plaza Mayor in Valladolid has a perfectly rectangular shape, with a length of 122 meters and a width of 82 meters, establishing a 3 x 2 proportion. It is the first square of its type built in Spain, closed and with a regular plan. It will serve as the model for the central square in Madrid, built in 1617, and for the one in Salamanca, built in 1729, where the Valladolid architectural and urban pattern reaches its perfection. A long series of squares in Spain and South America are inspired by these latter two, thus indirectly pointing to the square in Valladolid.On the 21st of September 1561, a widespread fire engulfs Valladolid and burns for three days. The disaster is nonetheless a chance for applying new urban ideas. The project of the new square follows the principles of Renaissance balance and symmetry. The square is thought as a closed, rectangular space, completely hollow in the middle, with entrances through porticoes. The architect Francisco de Salamanca projects identical, mirror façades. Behind them there are living spaces for the functionaries and the members of the guilds. On the ground floor, all around the square, one finds a colonnade.