Fuerte San Miguel ( Uruguay ) Fuerte de San Miguel is a military fortification in the small town of Dieciocho de Julio in the Rocha Department of eastern Uruguay . It was erected in 1737 by the Portuguese , having abandoned the attempt at building a fort in Maldonado . It was constructed of large , heavy stones to create the tall towers ( four bastions ) , thick walls and sturdy ramparts to withstand the onslaught of wars fought against the Spanish invaders which was instrumental in Uruguay evolving as an independent nation . Geography . The fort is located on Route 19 , south of the Laguna Merin , and west of Chuy . Visible after passing Paso de Punta Segra , it is situated on top of the Sierra de San Miguel , thirty - five metres high , in an area of mostly large and extensive valleys . At the foot of the mountain runs the San Miguel River , though it is out of sight of the fortress . In the distance are mountains forming the boundary with Brazil . History . With a garrison of 100 men , the fort was used by the Portuguese as an observation post of the movements of the Spanish forces . Article XVIII of the Treaty of Madrid ( 1750 ) decided that Portugal would keep the line of Castillos Grande , and could strengthen it . Before the signing of the Treaty of El Pardo ( 1761 ) , the governor and captain - general of the captaincy of Rio de Janeiro , Gomes Freire de Andrade , anticipated the consequences for the South and ordered the governor of the Colony of Rio Grande de São Pedro , Colonel Elói Madureira , to immediately dispatch troops to the Laguna region . The Portuguese strategy was to quickly build a fortified defensive line , south of Fort San Miguel , to stop the Spanish invasion in progress , after the conquest of Colonia del Sacramento in October 1762 by Governor Pedro de Cevallos of Buenos Aires . In October 1762 , construction of the Fortaleza de Santa Teresa began nearby to surpass San Miguel as the main Portuguese stronghold . In April 1763 , Ceballos took San Miguel and the Spanish improved it considerably into a fully functioning fort . In 1775 engineer Bernardo Lecocq made reinforcement works to the structure of the fort , with a British invasion imminent . With the Treaty of San Ildefonso ( 1777 ) , the Spanish were legally confirmed as being in possession of the fort . In 1797 , the fort reached its peak as a stronghold when it was strengthened further , again in anticipation of war . After Uruguayan independence in 1828 , the fort was deactivated and abandoned , becoming a ruin over time . By 1891 , the fort was covered with plants , forming cracks ; in one corner , a mountain palm ( " Cocos australis " ) was growing . Architecture . Initially designed as a simple defence base , building started on 17 October 1737 by the Portuguese ( although the monument itself implies it was built between 1734 and 1737 ) , attributing its construction to the military engineer Brigadier José da Silva Pais and the Portuguese military architect Manuel Gomes Pereira , later replaced by Captain Antonio Teixeira Carvalho . The fort is of smaller proportions than the neighbouring Fortaleza de Santa Teresa , being of lesser quality and irregular finishing due to the lack of granite stones available . The initial plan had the shape of a rectangular stone polygon with two pentagonal bastions on the shorter sides at the corners , separated by curtains , and topped by watchtowers . By 1740 , the base had developed , featuring a star format with four bastions pentagonal vertices in Vauban style , with internal walls and service buildings erected in irregular stonework . There was a chapel on the mound , and on one of its sides , there is a deep well . The perimeter of the walls total . Access to the fort was by a drawbridge over a flooded moat . In one of the slopes of the hill that is covered with living vegetation , there is a notable outpost ; facing to the east , it includes a wall with a small window , but its appearance is natural , like a cave or animal shelter . However , over the years after the independence of Uruguay , the fort ' s walls started crumbling as it remained untended . Uruguayans , proud of the historical heritage of the fort of more than 300 years for the founding of Uruguay as an independent nation , decided to get the hill top fort restored in 1927 . The history and structure of the fort were thus rescued by a committee composed of Gen . Alfredo R . Campos , General Alfredo Baldomir and historian Horacio Arredondo , which began operating in 1927 . In 1933 , the fort was rebuilt according to original plans , using the techniques of the time , restoring the premises of the Command House , the Parliament House , the chapel , kitchen and Troop Barracks . The fort was declared a National Monument of Uruguay in 1937 , thereafter to promote the recovery process . As a protected area , the diverse natural ecosystems has also been retained where native wildlife of Monkeys , birds , capybara s and guazubira are seen in the forests and marshland . Features . Under the administration of the Army , the structure is permanently open to visitors , harbouring a Museum of Military History , which highlights the collection of historical uniforms of the garrison , and the sample of the historical evolution of Army uniforms . A series of watercolors by artist Emilio Regalía are on display . Near the fort is the inn , Hosteria Fortin de San Miguel , a 1945 building built in the Spanish colonial style with 20 rooms and a ballroom that can accommodate 150 people .