Belem Tower. View of Belem Tower, Lisbon, Portugal, at night. This tower was built on the banks of the Tagus River between 1515 and 1521 by King Manuel I of Portugal. It was designed to guard the Port of Lisbon and commemorate the voyages of exploration made from here by Portuguese sailors and navigators, such as Vasco da Gama's voyage to India in 1497-9. These voyages took place in the 15th and 16th centuries during what is now called the Age of Discovery. The tower and the nearby Jeronimos Monastery form a UNESCO World Heritage Site.