 They were defending against a much larger Soviet force with over 6,000 tanks, twenty times the number the Finns had; but they had terrain that was broken up by lakes and forests, so tank movement was restricted to roads and tracks.Their defensive line, the Mannerheim Line, integrated these natural defenses with mines, including simple fragmentation mines mounted on stakes.While the Germans were advancing rapidly using "blitzkrieg" tactics, they did not make much use of mines.