15. Seal of San Sebastian (c. 13). It shows a battlement fortification, with towers at either end, a barbican at the entrance and a heraldic tower. It is probably a generic representation of a castle and not necessarily the one built on Mount Urgull.© Xabi Otero

At the western end of the Pyrenees, close to the Bay of Biscay, the landscape becomes gentler, in theory making it easier for an invading army to cross the Franco-Spanish border into Gipuzkoa at this point. It was for this reason that the towns of Hondarribia and San Sebastian were fortified from the sixteenth century on and were to become important strongholds.

The series of civil wars waged in Spain in the nineteenth century and the defence plans approved after the second of these led to the building of further fortifications - some provisional and others permanent - in the north-east of Gipuzkoa. It is for this reason that most of the fortifications dealt with in this book are concentrated in such a small area.