On 9th of April 1940 the German army and navy attacked Denmark and Norway without warning. The armed forces of both countries were outnumbered and there really wasn’t much hope of successfully defending against the attack. The Danish armed forces surrendered in a matter of hours while the Norwegian forces kept fighting for a while helped by the fact the transport of the German forces over land delayed the attack somewhat and the Norwegian landscape were more favorable for the defenders. Despite the continued war in Norway the southern part of the country was quickly overrun by the German army and the Germans quickly reached the border to Sweden.
The main reason for the German assault on Denmark and Norway were a wish to protected the shipment of Swedish iron ore to Germany. The iron ore were shipped out at the Norwegian harbor of Narvik which never freezes over during the winter unlike the Swedish harbors. The iron ore shipment was considered critical to the German war effort and to Hitler the Swedish mine in Kiruna along with the oilfields in Romania were the most important sources of raw materials for the war.
The attack on Denmark and Norway meant the German army and navy now were right next to pretty much all of Sweden and the country was vulnerable to a German attack. Considering Germany attacked Denmark and Norway to secure the control of the Swedish iron ore shipment the possibility of an attack on Sweden was certainly real. The Swedish government decided to give Germany the right to transport troops through the country at will and they continued the iron ore shipment to Germany for the duration of the war – so an attack never happened.
In addition to the appeasement of the Germans the Swedish government figured some military deterrent would be appropriate as well. One of the places to make such a deterrent was at the border region of Bohuslän which is located right at the border to Norway and on the approach to the second biggest Swedish city Göteborg. This area was an obvious point of attack in case the Germans decided not to respect the Swedish neutrality anymore.
The road to Norway ran along the Parse Lake so a German – this was a natural bottleneck for a possible German attack towards Göteborg so it was natural to make a stronghold at this point in the hope of delaying a possible attack. To help the defenders the Swedish military started to build a fortification at this location shortly after the attack on Norway in April 1940 and several minor bunkers and machinegun positions were constructed at a small hill next to the road and the lake. There were some fortifications built at the road itself during the war as well.
The fortifications at the road itself were removed after the war to let the traffic pass through the area again. The fortification on the hill has been left more or less intact – it was probably too difficult to demolish these old concrete constructions so they have been left until this day. You can stop at the parking lot right across from the fortifications and walk to the top of the hill to see the old fortifications – fortunately they were never actually used since the Germans never actually attacked Sweden.