Sand, peat, stone and concrete

Earthworks were first built using sand and peat, partly on top of the bastions and other fortifications dating back to the Swedish era. Wooden firing platforms first built were gradually replaced with stone foundations for guns, and the parapets of batteries were reinforced. Temporary gunpowder magazines and ammunition storages built during the war were also refurbished and reinforced. Casemates dating back to the Swedish era were adjoined to new forts, serving as ammunition storages. Under the reforms undertaken by the Russians, the basic structure of the gunpowder magazines dating back to the Swedish era were retained unchanged but they were strengthened by covering them with a layer of soil.

Initially, earthworks were built in a zigzagging geometric pattern, with fire direction and mortar platforms being placed on top of them. Between the gun emplacement, connecting corridors and shelters for crews were built. The soil brought from outside Viapori for the earthworks also contained seeds of various invasive plants These plants still thrive in Suomenlinna.

The chain of earthworks and gun emplacements was extended to both sides of the Viapori main islands. In the west, earthworks extended to the island of Harakka, in the east, to the island of Santahamina. Following developments in armaments, explosives and construction technology, the Russians sought to build increasingly strong buildings, in which process concrete was also used. Equipping the fortress with increasingly effective guns was expensive, causing the reforms to make slow progress.