Meet Belém’s (or St. Vincent’s) Tower.
“It’s a fortified tower in the [borough of Belém,] municipality of Lisbon, Portugal. It is a UNESCO World Heritage Site 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 defence 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 a 30 m (100 foot), four floor tower.” So does Wikipedia says.
It was sheer luck that, during the walkabout I took this photo on, a sail boat was passing by and it look fairly old and had a Latin sail, similar to the ones used by the Portuguese back in the 16th century.