The pillbox, a standard enclosure
providing excellent protection, was constructed of such durable
materials as concrete and rebar. As
the art of shelling advanced,
defenders were driven into ever more hardened positions.
In the USSR, a great many bunkers were strengthened along the "Molotov Line," a system of defensive fortifications stretching about 100 km. It was created to replace the "Stalin Line," as the boundaries of the USSR expanded with the accession of the Baltic States, Belarus and western Ukraine. This new line stretched from the Baltics to the Carpathians. The size of these pillboxes depended on the facilities and weapons required. Some held 8 to 10 troops, while the larger ones fit 30 to 40 men.