Short answers, pulled from the story.
Construction work on the Karelian Isthmus began in 1920 after Bolsheviks won the Russian Civil War. The line remained incomplete by November 1939 when the Winter War started despite increased funding since May 1938.
Lieutenant Colonel A. Rappe presented a defensive line plan to Finnish high command in May 1918. Johan Fabritius commanded the second construction phase that started on the 1st of April 1934.
The line stretched from Gulf of Finland coast through Summa to Vuoksi River ending at Taipale in east. It consisted of one hundred fifty-seven machine gun positions and eight artillery positions built primarily from concrete.
Purpose remained delaying invasion rather than completely repelling enemy forces through static resistance. Methodology applied flexible defense principles using trenches and obstacles instead large permanent bunkers.
Finnish funds resources supported only one hundred one concrete bunkers compared to five thousand eight hundred structures along equivalent Maginot Line length. Amount concrete used in whole Mannerheim Line slightly less than amount used in Helsinki Opera House building.