Fortified district

A fortified district or fortified region (Укреплённый район, Укрепрайон, ukreplyonny raion, ukrepraion) in the military terminology of the Soviet Union, is a territory within which a complex system of defense fortifications was engineered.

Each fortified district consisted of a large number of concrete bunkers (pillboxes) armed with machineguns, antitank guns and artillery. The bunkers were built in groups for mutual support, each group forming a centre of resistance. The area in between was filled with various barriers and obstacles, as well as mine fields. A dedicated military unit (Fortified district troops) was permanently assigned to man each region.

The concept of ukrepraions was developed during the Russian Civil War, when large territories were to be defended by relatively sparse military force. The first military units named so appeared in 1923.

In 1928 the program for the construction of the comprehensive system of fortified districts was launched. It started with 13 fortified districts, which over the time have evolved into the Stalin Line.