The military-historical complex "Kollasjärvi" is situated 30 kilometres from the town of Suojärvi on the way to the village of Loimola. During the Second World War it's territory has been the theatre of severe battles of the Soviet and the Finnish troops. At present the remnants of both the Soviet and the Finnish fortifications have been preserved: trenches, hollows, dugouts, numerous graves of the remains of the Finnish, Soviet and German soldiers.

During "The Winter War" the Finnish soldiers stood to death defending their Motherland. To honour the memory of those, who lost their lives, "The Cross of Mannerheim" was erected on the 10-th km. from the village of Loimola. Finnish citizens and regular troops of the Finnish army took an oath of faithfulness by "The Cross of Mannerheim".

At the present time the cemetery of the Finnish soldiers and the memory sign are situated on the territory of the complex "Kollasjärvi", they are often visited by Finnish sitizens.

In the history of the events of the World War II 1939-1945 in Karelia one of the most significant places is taken by the fights in the region of Kollasjärvi (the Suojärvi district, to the north from the railway station of Loimola).

During the Soviet-Finnish War 1939-1940 this territory was in the zone of the offensive action of the 56th and the 75th infantry division of the 1st Corp 8th Army (Army commander – division commander I.N.Khabarov, and since February 1940 – Army commander G.M.Shtern), who lead fighting operations along the right flank of the Loimola direction.The Soviet troops were resisted by units of the IV Finnish Army corps (commander – major-general Ju.Heiskanen, since the 4th December 1939 – major-general V.Hägglund) and Rasanen group. The Soviet troops aimed to capture the railway station of Loimola, gain the rear of the Pitkäranta Finnish group and later assume the offensive action to Sortavala.

On the 30th km. of the Suojärvi – Loimola road there was a very powerful strong point of the Finnish defence – the height "Chyornaya" ("Black", the hill Kollaa). A famous Cross "Kollaa" (12 metres high), unofficially called "The Cross of Mannerheim" was erected here. Finnish inhabitants and regular Finnish troops took an oath of faithfulness in front of this Cross.

Within the period of the 4th December 1939 – the 10th March 1940 this area was the theatre of furious fighting. Three Soviet soldiers – V.I.Ivanov, V.P.Parfenov and A.A.Rozke – were awarded a title of a Hero of the Soviet Union for courage and bravery when taking by storm the height "Chyornaya". However it was impossible to overcome Finnish defensive positions at Loimola.

On the 16 December 1939 Finnish troops began a counter-attack and captured a bridge-head on the eastern river bank Kollanjoki, but failed to prolong this success. Heavy fighting on the border of the lake Kollasjärvi and upper reaches of the river Kollanjoki were being continued until the end of the war. In March 1940 in the region of the height 187.9 (to the north-west of the lake Suolampi) the 75 th infantry division suffered heavy losses. According to the archive materials a common burial place of the Soviet soldiers is situated here, but the exact place has not been revealed yet.

According to the Peace Treaty of 12 March 1940 the territory of the Suojärvi district was withdrawed to the Soviet Union.