Oiasso, Oiasona or Oiarso was a Vascon Roman (Civitas) town located on the left bank of the Bidasoa estuary in the Bay of Biscay. Archaeological evidence unearthed recently pinpoints the core area of Oiasso in the old quarter of Irun (Gipuzkoa) by the Spanish-French border, where harbour and bath remains have been discovered. However, two other focuses in Cape Higuer and hermitage Ama Xantalen point to a wider complex outside the main nucleus.

Irun is a town of the Bidasoaldea region in the province of Gipuzkoa in the Basque Autonomous Community, Spain.