El fortín de Usila y el Cinturón de Hierro Historical milestone · Ugao-Miraballes, Arratia-Nerbioi, Bizkaia Image of Ugao-Miraballes, not of the place itself. Beneath the railway bridge stands the Usila fortlet, built in 1937 as part of the Cinturón de Hierro (Iron Belt), the defensive system that protected Bilbao during the Civil War. 1937 Photo: Txo (CC BY-SA 4.0) What to see and do in Ugao-Miraballes