 Many Basques from Biscay proper, Gipuzkoa, Álava, and even Navarre joined Charles V's forces, as did a number of Aragonese.Ahead of the Castilian expedition to the Bidasoa, a combination of Gipuzkoan militias supported by 1,000 landsknecht engaged the Franco-Navarrese at the fortress of Urantzu in the celebrated Battle of San Marcial.The pro-Imperial forces took the position on 30June 1522.