the mannerheim line was the best, most well fortified defensive line in europe. better than the maginot line because the planners looked at that and tried to make a better one.

the soviets smashed through that in months in one of the worst conditions you can have. finns have nothing to be proud of.

But the keystone to the Finnish defensive arch was the famous Mannerheim Line on the Karelian Isthmus based on the second largest industrial town in Finland, Viborg (Viipuri), The right of this formidable system of fortifications rested on the sea in The forward the Gulf of Finland and its left on Lake Ladoga. The forward zone was within 21 miles of Leningrad, the second largest city in the U.S.S.R. with a population of over three million inhabitants. If, as Napoleon had said, “ Antwerp is a pistol held at England's head,” what was the Mannerheim Line to the Soviet Union in these days of modern long-range artillery?

The Mannerheim Line had been constructed with the best military advice, including that of the British General, Sir Walter Kirke, who had given it a final inspection june, 1939. In the early Finnish communiques it was referred to as Ihe Kirke-Maginot Line. Based on a plan similar to that of the Maginot Line, it incorporated what that passive defence system lacked, the ideas of the more active defence of the Siegfried Line. Thus, it could be used when the 'time was ripe, for offensive action; as visualised in the “ Hoffman ” plan, cherished by Germany for her Baltic invasion of the U.S.S.R. up to August, 1939.

There were three zones in this system. The forward zone of a depth varying from three to eight miles and consisting of concrete block-houses and pill-boxes, equipped with machineguns, anti-tank guns and field artillery, and guarded by barbed wire, anti-tank traps and land mines.

The second zone, the main line of defence was some 70 miles in length, and ran from its “right on the coast fortress of Koivisto, across Lake Muolaa, then along the Vuoksi waterway and finishing with its left at the fortress of Taipale at the mouth of that river on Lake Ladoga. It was seven miles in depth except in the lake districts, where it narrowed to two miles. The fortifications of this section were two-storied in depth, embedded in the ground and constructed of reinforced concrete and armour plate. Armed with heavy artillery, each fort was capable of independent defensive action. All were protected by barbed wire, trenches ,tank traps and land mines. There were in all 350 two-storey reinforced concrete underground forts and 2,257 granite emplacements.

The third zone was centered on the rail junction and industrial town of Viborg and was a special fortified area of some 25 miles in circumference.

If military thought considered the French Maginot Line impregnable from frontal assault, and the German Command evidently did think so or they would not have gone round through Belgium as they did, this Mannerheim Line with its flanks secure would have been even more so.

from here