Plans for the fortifications were prepared by Lieutenant-Colonel Augustin Ehrensvärd, who was also tasked with constructing the fortresses in 1747. Construction started in 1748 and continued with increasing tempo as the external political situation deteriorated in 1749 and 1750. Over half of the Swedish army in Finland was tasked with the construction and in 1750 more than 6,000 men were working on the fortifications at Svartholm and Sveaborg. Ehrensvärd had tasked first Captain O. R. Clansenstierna and later (1751-1757) Lieutenant-Colonel Fabian Casimir Wrede with the construction efforts at Degerby and Svartholm who had in 1751 around 2 000 workers at their disposal. While the plans for the fortifications around the town had to be cut short it did not hinder the construction of Svartholm. King Adolf Frederick visited the site in 1751 which was renamed from Degerby to Lovisa () after his wife Louisa Ulrika during his reign. Like at Sveaborg the Swedish participation to the Seven Years' War brought construction effort to a standstill.