The first newly constructed fort of the defensive ring was situated near Abcoude and completed in 1885. It consisted of shellproof military barracks, depots and open artillery deployments, surrounded by earth walls. The entire complex was surrounded by a moat. The idea was to apply this design throughout the entire Defence Line of Amsterdam. This era also saw the invention of the high-explosive shell, though, which greatly decreased the defensive value of this type of fortress. The construction of the other forts was therefore put on hold for the time being, awaiting a new, adapted design.