Belém Tower or the Tower of St Vincent is a fortified tower located in the civil parish of Santa Maria de Belém in the municipality of Lisbon, Portugal. It is a UNESCO World Heritage Site (along with the nearby Jerónimos Monastery) because of the significant role it played in the Portuguese maritime discoveries of the era of the Age of Discoveries. The tower was commissioned by King John II to be part of a defense system at the mouth of the Tagus River and a ceremonial gateway to Lisbon.
The tower was built in the early 16th century and is a prominent example of the Portuguese Manueline style, but it also incorporates hints of other architectural styles. The structure was built from lioz limestone and is composed of a bastion and the 30 meter (100 foot), four story tower. It has incorrectly been stated that the tower was built in the middle of the Tagus and now sits near the shore because the river was redirected after the 1755 Lisbon earthquake. In fact, the tower was built on a small island in the Tagus River near the Lisbon shore.
In the late 15th century, King John II had designed a defense system for the mouth of the Tagus that depended on the Fortresses of Cascais and São Sebastião (or Torre Velho) in Caparica on the south side of the river. These fortresses did not completely cover the mouth of the river and further protection was required. In the first half of the 16th century, in the "Chronicle of John II", the author Garcia de Resende, affirmed the monarchs opinion that the defenses of Lisbon were insufficient, and that he had insisted on providing efficient fortifications along the entrance to the Tagus River to supplement the existing defenses.
The Tower is situated on the northern bank of the Tagus River in the civil parish of Santa Maria de Belém, municipality of Lisbon, accessible at the western end of the Avenida de Brasília. Nearby are the Monastery of the Jeronimos (to the east) and the Fort of Bom Sucesso (to the west), while to the north are the Tower Governor's residence, the old Governor's residence for the Bom Successo Fort, and the Chapel of São Jerónimo . The Tower itself is accessible via the Avenida de Brasília and by a small bridge that extends over the water to the structure.
Its plan is composed of a rectangular tower and an irregular, hexagonal bastion, with elongated flanks, that projects south into the river. It is basically a large articulated vertical space resting on a horizontal mass/slab, covered by exterior enclosures. On the north-east angle of the structure, protected by a protective wall with bartizans, there is a drawbridge to access the bulwark, decorated in plant motifs, surmounted by the Royal coat of arms and flanked by small columns, complimented with armillary spheres.
The interior part of the bastion cave, with a circular staircase in the north, has two contiguous halls with vaulted ceilings supported by masonry arches, with four lockers and sanitary installations. On the ground-floor bunker, the floor is inclined towards the outside, while the ceilings are supported by masonry pilasters and vaulted spines. Gothic rib vaulting is evident in this casemate, the rooms of the tower and the cupolas of the watchtowers on the bastion terrace.