Ruinas das Muralhas do Castelo de Seda

Portugal, Portugal

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Ruínas das Muralhas do Castelo de Seda near Alter do Chão in Portugal's Alto Alentejo originated from a Romanized castro on the Ribeira de Seda, evolving into a medieval fort named Arminho under Muslim rule before conquest by Afonso Henriques in 1160, who donated it to the Knights Templar and later to the Order of Avis in 1271 under Friar Simão Soeiro.

The oval enclosure featured schist walls with three surviving circular cubelos (towers) and remnants of a fourth, protecting a small settlement amid Reconquista frontier skirmishes until municipal extinction in 1836. Partial collapses in 1970 prompted DGEMN consolidations in 1971 and 1978, classifying it as a Property of Public Interest in 1982 amid rural vegetable gardens and steep slopes.