in early 1915 it was decided to build new defenses further away from the city center. the new defenses were stronger fixed fortifications with positions quarried into rock or dug into ground. fortifications were built from wood and stone masonry as well as concrete. new fortifications had a network of defensive structures, with trenches, rifle pits, machine gun nests, barbed wire obstacles, shelters and roads. artillery batteries were located behind the front line, often located on reverse slope. artillery batteries had 2-6, typically four, guns. heavily fortified caponiers providing flanking fire were built on places of the front line. first a northern line was built at leppävaara-kaarela-pakila-pukinmäki-myllypuro-vartiokylä. construction on a western line from leppävaara to westend via tapiola began shortly afterwards. in late 1915 it was decided to build an outer line of defence on the northern and eastern sectors, extending the fortifications northward and in the east from pukinmäki to malmi, mellunkylä and vuosaari. fortification works continued until the february revolution of 1917, and some work was done until early 1918. the land front was divided into three sectors, eastern, northern and western with 36 bases, numbered i-xxxvii. the bases were usually centered on hilltops with the strongest defences.<ref name="vallihaudat/linnoitteet"></ref>