The Krepost Sveaborg was an Imperial Russian system of land and coastal fortifications constructed around Helsinki during First World War. The purpose of the fortress was to provide a secure naval base for the Russian Baltic fleet and to protect Helsinki and block routes to Saint Petersburg from a possible German invasion. Krepost Sveaborg was part of the Peter the Great's Naval Fortress, a coastal fortification system protecting access to Saint Petersburg by sea. The central part of Krepost Sveaborg was the old fortress of Suomenlinna where the fortress headquarters were located. Due to technological advances in artillery the old fortress was no longer capable of providing a sufficient protection, and a new main defensive line was built well beyond the old fortress boundaries. New coastal artillery guns built on outlying islands protected Krepost Sveaborg from the sea, while fortified lines constructed around Helsinki were intended to stop any attacks on land. The primary coastal guns were 10 in (254 mm) model 1891 guns and 6 in (152 mm) model 1892 Canet guns. Older 11 in (279 mm) model 1877 guns were also used. In summer 1917 the fortress had two hundred coastal or anti-landing guns, of which 24 were 10-inch guns in six batteries, 16 were 6-inch Canet guns in four batteries and twelve were 11-inch guns in three batteries. The artillery used in land fortifications included older coastal guns, old fixed carriage guns and newer light field guns.