Castle of Alter do Chão

Portugal, Portugal

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Castle of Alter do Chão in Alter do Chão, Portugal, traces its origins to a Roman settlement atop an Iron Age site, evolving into a Moorish fortress before Christian conquest in the early 13th century under King Afonso II, who ordered repopulation in 1216.

Rebuilt in 1357 by King Pedro I—with a commemorative marble plaque above the main gate—and granted privileges akin to Santarém by Dinis, it passed through noble hands including Nuno Álvares Pereira and the House of Braganza after Manuel I's 1512 charter.

This Gothic quadrangular stronghold with cylindrical corner towers and a prominent arched gateway defended the Alto Alentejo frontier, later serving as a prison under João II before private ownership in the 19th century.