The forts erected by Liberal troops during the last civil war of the nineteenth century were stronger than those of the First Carlist War. Stonework was more widely used and some of these erections might be considered to be permanent or semi-permanent fortifications although they were nonetheless far from offering the advantages of the mighty French forts of the time.

Some were relatively large and contained a significant number of embrasures for close-range defence as well as plentiful supplies of gunpowder. They were defended by a fosse, sometimes flanked by double caponiers (batteries located in the fosse which did not protrude from it) and a drawbridge. They had barracks, ammunition dumps, a cistern, latrines, etc. There were forty-six such constructions in the North East of Gipuzkoa, facing a similar number of Carlist forts (which were generally less sophisticated).

Some of the liberal fortifications were built at the initiative of the municipal authorities; on others cases, advice was given by the Engineering Corps (in which case the municipal authorities were entitled to recover any investments they had made in them). Others were executed directly by the Engineering Corps, although they sought contributions from the municipality in terms of materials and labour.

98. St. Barbara Fort (Hernani) around 1930.© Indalecio Ojanguren

During the war, the municipal authorities spent 984,307 pesetas on fortifications and, like many private individuals whose interests were affected by the fortifications, they often had to go to considerable lengths to claims the amounts they were owed by law.

99. St. Barbara Fort in the Third Carlist War:
1-Round telegraph tower;
2-Entrance to the tower;
3-NW battery;
4-Ramp leading to the NW battery;
5-Steep double caponier linking the two sites in the fort;
6-Entrance to the fort;
7-Beds;
8-Barracks 1;
9-Dining area;
10-Kitchen;
11-Latrines;
12-Stairs leading to the officers' quarters;
13-Provisions store;
14-NE Battery;
15-Ammunition dump;
16-SE Battery;
17-Barracks 2;
18-Cistern;
19-Barracks 3;
20-Banquette;
21-Ramp leading to the SW battery;
22-SW Battery;
23-Corps de garde (sergeant);
24-Corps de garde (troops);
25-Upper crenellated platform;
26-Fosse.© Juan Antonio Sáez

The troops defending the liberal San Sebastian during the Third Carlist War depended on three lines of provisional fortification hurriedly thrown up around the city (the walls had been demolished in 1864). The first, and closest to the Carlist lines, was mainly comprised of the Calvary tower and the Hernández, Artola, Farola, Lugaritz, Puyo, Ametzagaña, Miracruz and Admiral forts. The second line, further back, consisted of the Old tower, the Windmill and Pintore forts, the Loyola tower and the Concorrenea fort.

The third fortified line ran around the urban nucleus of the city. It consisted of a crenellated wall of ordinary masonry backed by various adjoining bunkers and guardrooms and by the fortifications on Mount Urgull.

Significant fortifications were also constructed around the urban centres of other towns: Hernani, Irun, Tolosa, etc., featuring masonry walls and wooden gates blocking the streets. Garden walls and buildings in the town, reinforced with crenellated tambors or small artillery batteries, were also used as improvised defence walls.

Unlike the fortifications built during the First Carlist War, important remains of some forts (the Ametzagaña, St. Barbara, Mendizorrotz, Oriamendi, Lord John Hay, Admiral forts, etc) and towers (Jaizkibel, Elatzeta, Zubelzu, etc.) are still standing. This is because after the war they were classified according to their military importance, and some remained active or on reserve for a number of years afterwards.