The initial idea for strengthening the defense of the mouth of river Tagus with the construction of a Tower, the Torre de Belém, comes from the time of D. João II (1481-95). The structure would only begin in 1514, under the reign of D. Manuel I (1495-1521). Master Boytac (master of the works of the Kingdom) who worked at the Jerónimos monastery in Belém since 1502, and was initially called to this work. Something did not go well with Boytac in its participation in the recovery of the defenses of Arzila in 1509-10, and D. Manuel delivered this military work to the architect Francisco de Arruda, a specialist in defensive structures, with proven evidence in the continent and Africa. It was located on a rocky outcrop in the waters of the river, opposite the old beach of Belém, and was intended to replace the old artillery ship, anchored in that stretch, the S.Cristovão, which weighed 1000 tons. With the evolution of the means of attack and defense, the structure was gradually losing its original defensive function. Over the centuries it was used as a customs register, a telegraphic signaling station, and a lighthouse. Their storerooms were used as dungeons for political prisoners during the reign of D. Filipe I (1580-98), and, later, by D. João IV (1640-1656). The Archbishop of Braga and Primate of Spain, D. Sebastião de Matos de Noronha (1636-1641), by coalition to Spain and facing D. João IV, was arrested and sent to the Tower of Belém. It is an icon of the architecture of the reign of Manuel I of Portugal, in a synthesis between the keep of medieval tradition and the modern bulwark, where artillery pieces were available.