to other merchants who went to the "Great Exhibitions of the Kingdom" that took place in Medina. His fame as a physician exceeded the boundaries of Medina, and he practiced in Burgos, Segovia, Ávila and other important cities of Castille. He even came to the court of Phillip II where he was summed to attend upon Prince Charles, heir to the unfortunate throne, who had suffered a serious accident. Thanks to Pereira, the Prince lived until 1568. He was also interested in the construction of hydraulic devices and, with his companion Francisco Lobato, designed a watermill dam that could function without water, which was patented in 1563. In folio 26 of the Manuscripts of Francisco Lobato, the Medinan engineer decided to design a special mill, at the initiative of King Maxmilian II of Austria, who at the time was in Vallodolid (ca. 1550), a refugee from the wars against the Protestants. The future king of Bohemia took a fancy to go up the Douro River, so he commanded a galley be built and ordered the removal of any building that disrupted his navigation, i.e., fisheries and mills. This greatly harmed the locals who came to Lobato and Pereira to design a mill that could grind with the force of water without being directly on the river bank. Lobato goes on to explain that a model they tested on the Zapardiel River "milled and shook with reasonable force…, but it sucked in so much water that, by midday, there wasn't a single drop." Although the model was refined with a dam that returned the water to the river, the king paid no attention, and the project fell into oblivion. Lobato complained bitterly that, despite the promises of funding by the Habsburgs, "we have already spent 150 ducats…and he never paid me anything—someday I'll have to ask for it." Pereira's unique thought arose from his synthesis of philosophy and medicine. He rejected the authority of the old masters and medievals in favor of reason, logic and experience. Moreover, he often used paradoxes and syllogisms to expose the errors of those he questioned. Thus, it can be argued that his philosophy was more negative than positive, but this is understandable considering the context of ideological suppression in the face of religious authority, as well the veiled accusations about Pereira's Jewish origins. The famous essayist Menéndez Pelayo wrote of this famous thinker: In experimental