Castillo de San Esteban de Deyo o de Monjardín

Spain, Spain

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Castillo de San Esteban de Deyo, also known as Castillo de Monjardín, is a 10th-century fortress atop a 890-meter hill near Villamayor de Monjardín in Navarre, Spain, originally fortified by the Moorish Banu Qasi family from Tudela and conquered around 908 by King Sancho Garcés I, marking a key advance into the Ebro Valley.

Renowned as one of Navarre's most impregnable strongholds, it served as a royal pantheon with legends claiming burials of Sancho Garcés I and his successors, changed hands between the crown, church, and nobles like the Medrano family, and saw action in sieges by Charlemagne and Abd al-Rahman I, the 1512 conquest, and 19th-century Carlist Wars. 

Today, its ruins include the 16th-century Ermita de San Esteban de Deyo amid panoramic views of up to 60 Navarrese villages, drawing hikers along the Camino de Santiago for its historical significance and strategic prominence.