The four reinforced concrete fortifications (caponiers or pillboxes), built 1936–1938 by the Latvian Army Sapper Regiment, were an element of the Riga coastal defence system of the Latvian Army. These were designed to fire machine guns at a possible enemy landing in two different directions at the mouth of the Gauja River, which has since changed its location. Two special armoured trains, which could offer artillery support from Jūrmala to Saulkrasti, were also a part of the system.