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Guimarães Castle - Located in the northern city of Guimarães, this 10th century castle is a national landmark, and is considered the birthplace of Portugal.

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Silves Castle - Probably Roman in origin, this enormous red sandstone castle, located in the Algarve market town of Silves, was later occupied by the Moors between the 8th and 13th centuries.

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Almourol Castle - This picture perfect medieval castle is perched on top of Almourol islet, in the middle of the Tagus River, near the village of Vila Nova da Barquinha.

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Monsaraz Castle - The sturdy walls of this 12th century hilltop castle enclose ancient Monsaraz, one of the Alentejo's prettiest towns.

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Santa Maria da Feira Castle - A fine example of medieval military architecture, this well-preserved castle is found in Portugal's Aveiro district.

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Marvão Castle - Standing in the Alentejo near Portugal's border with Spain, Marvão Castle dates back to the 8th century.

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Penedono Castle - The lichen-covered walls of this imposing castle give it a weathered look that befits its long history. The medieval town of Penedono is located in Portugal's central northern reaches.

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Óbidos Castle - The already picturesque town of Óbidos, with its whitewash cottages and terracotta roofs, is further enhanced by this little gem of a medieval castle.

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Mértola Castle - Mértola is classified as a museum town. Its 13th century castle is the icing on the cake.

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São Jorge Castle - Lisbon's landmark castle is also one of the city's most popular visitor attractions. Views from the sturdy ramparts are simply jaw-dropping.

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Bragança Castle - Located in the far northeast of Portugal, Bragança is noted for its brooding granite-stone castle, which forms part of the 13th century citadel. (Photo: Wikimedia/CC BY 2.0)

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Belmonte Castle - Situated near the city of Covilhã in the country's Beira Baixa district, Belmonte dates back to the 12th century.

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Leiria Castle - The city of Leiria is noted for its impressive 12th century castle, which encloses a former royal palace.

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Loulé Castle - Known for hosting one of the busiest and most colorful markets in the Algarve, Loulé is equally celebrated for its well-preserved 13th century castle.

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Alegrete Castle - Set near the Alentejo town of Portalegre, this near-ruined defensive structure once served as an important lookout post across the vast plains stretching towards Spain.

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Evoramonte Castle - The Alentejo village of Evoramonte is dwarfed by the unusual rectangular shape, and circular towers, of the 12th century castle built to defend the community.

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Montalegre Castle - This castle is located in northern Portugal. It sits on a hill overlooking the peaceful town of Montalegre in the Vila Real district.

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Barcelos Castle - Little remains of the castle palace walls that mark the original entrance to this historic northern Portuguese city.

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Lindoso Castle - The stone used to build this 13th century stronghold is the same as that used to construct the unusual coffin-shaped structures set near the entrance.

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Tomar Castle - Tomar Castle forms part of the magnificent Convent of Christ complex, a UNESCO World Heritage Site.

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Sabugal Castle - Standing near the Côa River in central Portugal is this compact and handsome-looking castle, unusual for its pentagonal build.

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Sortelha Castle - Sortelha is one of the oldest and most beautiful towns in the country. Its medieval veneer is enhanced by the remains of a 12th century castle. (Photo: Wikimedia/CC BY 2.0)

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Numão Castle - Vestiges of the remote Numão Castle can still be admired, but you'll have to journey north towards Vila Nova de Foz Côa to admire what's left. (Photo: Wikimedia/CC BY-SA 3.0)

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Castle of the Moors - The Moorish castle in Sintra is set along a meandering granite escarpment high above the town, which is located northwest of Lisbon. The whole landscape is a designated UNESCO World Heritage Site.

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Montemor-o-Velho Castle - One of Portugal's most expansive military landmarks, the castle and its walls afford impressive views across this area of central Portugal. (Photo: Wikimedia/CC BY 2.0)

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Marialva Castle - The town of Mêda, in the central eastern district of Guarda, is the setting for this ruined but still alluring stronghold.

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Campo Maior Castle - Like so many other fortifications in the region, the 13th-century castle at Campo Maior in the Alentejo is orientated towards Spain as a first line of defense.  (Photo: Wikimedia/CC BY-SA 3.0)

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Porto de Mós Castle - Designed in the Romanesque style, this delightful medieval eye-opener can be found near the town of Mós, in the far northeast of Portugal. (Photo: Wikimedia/CC BY-SA 3.0)

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Viana do Alentejo Castle - Set well off the beaten track in the Alentejo heartland, this ornate Gothic structure is characterized by five cylindrical towers.

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Mourão Castle - Built during the Middle Ages, this castle is named after the sleepy Alentejo village of Mourão. (Photo: Flickr/CC BY 2.0)

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