Situated on the northern bank of the Tagus River, the fortified Belem Tower (also known as the Tower of St. Vincent), commissioned by King John II, was designed as part of the defensive system for the protection of the river's entrance. It played a significant role in the port's maritime "Age of Discoveries." Construction began in the early part of the 16th century. When completed in 1519, it was four stories (98 feet) tall. Spanish forces captured the city in 1580 and the tower was turned into a prison (until 1830). During the Peninsula War (1807 to 1814), French forces occupied the tower. By 1865, a beacon had been installed on the tower to aid ships navigating the river. Telegraph service also began from the tower around the same time. Belem Tower was designated a World Heritage site in 1983 and is open to the public as a museum.
As a side note; while visiting the Tower, we met a French contingent of the "Royal Order of the Khaki Vest" society. Who would have guessed?