The unique Belém Tower was built in 1519 in the river Tagus as part of a defensive system and to commemorate Vasco da Gama's expedition. The fortified tower has become one of the symbols of the city and is a major attraction. The Romanesque-Gothic structure was declared a National Monument in 1910 and classified, together with the nearby Mosteiro dos Jerónimos (Jerónimos Monastery), as a UNESCO World Heritage Site in 1983. A must see in Lisbon!