It was not an easy matter to construct forts on the soft peat soil around Amsterdam. The soil first had to be reinforced with large quantities of sand and pile foundations had to be laid – all at great expense and causing much delay. The sand was refashioned into defendable earthworks enabling some level of defence in case of an emergency. Work was carried out in stages from 1880 up to the outbreak of World War I. During that time, new insights on the construction of forts were incorporated into the Defence Line.

In those days, the Defence Line of Amsterdam was considered the most modern and most extensive fortress-building project in Europe. From 1885 the devastating effect of the recently invented high-explosive shell was taken into account when building forts. Consequently, a new type of fort was designed consisting of concrete, soil-covered bunkers instead of the brick forts which were still in use in the Dutch Inundation Line. Although the forts differed in size, the shape was basically the same - long and narrow - reducing the chance of being hit. The majority of the forts were equipped with armoured gun turrets. Another new feature was that they were built at approximately three-kilometre intervals, so that they could provide support fire (wide flank). This, together with the inundations, created a closed front around Amsterdam.

The left bunker of a fort. Two canons for wide flank and two machine-guns for close-range defence were mounted here.