Sweden seized the entire Baltic territory and the northern Baltic Sea as well as the Gulf of Finland in the Treaty of Stolbova (1617) and the Truce of Altmark (1629). Afterwards, it placed its naval attention on the southern coast of the Baltic Sea. The key military harbour of the navy moved from Stockholm to Karlskrona in 1680.
The defence of Finland and its coasts, though, was left extremely weak. The decision back lashed in 1659-57, when the Tsar of Russia Aleksey Mikhailovic began operating on Lake Ladoga with his barques and made surprise attacks on Karelia.
Due to these attacks, the Count of Raseborg, Gustaf Adolf Leijonhufvud commanded the Finnish peasantry to craft fortifications, at their own expense, in various locations: on Vargö island in front of Helsinki, at Porkkalan-niemi, in the Barösund archipelago and on the tip of the Hanko Peninsula. As a result, a field armament emerged in Tulliniemi’s Bruneskär (Skansholmen). The armament received a garrison of 55 soldiers, and it was commanded by Lars Hansson.
In conclusion, the memory that stays from the fortification is the name Skansholmen (Skanslandet) which still stands in the map of Tulliniemi. That the spot was excellent for defence was showed later, by the military armaments erected on the same cliffs.