Forte do Alto do Duque

Forte do Alto do Duque is a military fortress located in Belém at approximately 75 meters elevation on the southwestern edge of Monsanto Forest. The structure features a pentagonal design with a moat surrounding it.

The fortress was built between 1875 and 1890 as part of Lisbon's defensive line protecting the Tagus River from potential naval attacks. It represented a key element in the city's military infrastructure of that era.

The fortress marks the southwestern boundary of Monsanto Forest and stands as a visible reminder of Lisbon's military heritage. Its pentagonal design and stone structure form part of the city's architectural identity.

The fortress currently functions as headquarters for the Criminal Investigation Division of Lisbon's police and is not open to public visits. You can view the exterior from the forest edge, but access to the grounds is restricted.

In 1901, the fortress was the site of Portugal's first wireless transmission, sending a message across the Tagus River to Fort Trafaria. This marked an early moment in the nation's telecommunications history.

Location: Belém

GPS coordinates: 38.70374,-9.22209

Latest update: December 8, 2025 21:08