Forte do Alto do Duque

Perched atop a hill, the Forte do Alto do Duque commands attention. It watches over Lisbon. This isn’t just any fort. The Forte do Alto do Duque played a vital role in Lisbon’s defense. Construction began in 1875 and finished in 1890. The land belonged to the Duke of Cadaval, hence the fort’s name. The Forte do Alto do Duque became part of Lisbon’s Campo Entrincheirado, a defensive ring. Its mission, along with the Fort of Bom Sucesso, was to protect the Tagus River from attack. The fort’s design is unique. It has an irregular pentagonal shape, mostly built into the hillside, and surrounded by a protective moat. A central dome covers the main area. A separate barracks building, linked by a bridge over the moat, adds to the fort’s complexity. Officially, it is known as “Military Building No. 31 / Lisbon”. The Forte do Alto do Duque witnessed a historic event. In 1901, it hosted Portugal’s first wireless communication. A message was transmitted across the Tagus River to the Fort of Trafaria. The distance covered was an impressive 4,300 meters. During labor strikes in 1912, the fort served a different purpose. It was used to detain strikers, highlighting its role in maintaining order. The fort’s armament included four 15 cm SK L/40 naval guns made by Krupp. From 1932, a special detachment called the “Detachment of Alto do Duque Fort” was stationed there. In 1936, the fort saw action during the Spanish Civil War. It returned fire against Portuguese naval ships that rebelled. These ships attempted to leave the Tagus to support the Spanish Republicans against Franco. After the Carnation Revolution in 1974, the Forte do Alto do Duque briefly housed COPCON, a military command. This command was later dissolved after a failed coup attempt. The fort then became home to the Defence Strategic Information Service (SIED). Today, the Forte do Alto do Duque serves as the headquarters for the criminal investigation division of Lisbon’s Public Security Police (PSP). It stands as a testament to Lisbon’s rich history.