Known as the Castro culture, the Celtic people who once settled the northern parts of what is now Spain and Portugal from approximately the 9th century BC to the Roman era built extensive stone settlements and hill forts. Their distinctive circular structures are still found, centuries later, scattered across the modern countryside. 

The ruins at Castro de Baroña were rediscovered in 1933 near the fishing village of Porto do Son, and date to the first century AD. Twenty stone structures cover a rocky outcropping into the Atlantic, surrounded by the ruins of a double defensive wall. 

Other Castro future sites in Spain include Citânia de Briteiros near the Ave River, and Santa Tegra in A Guarda.