figurative sense is attested from 1832, from profit-and-loss accounting, where the final figure calculated is the bottom line on the page. Also (especially as an adjective) bottom-line, bottomline.
TO LINE BEES is to track wild bees to their homes in the woods. One who follows this occupation is called a bee hunter. [Bartlett, 1859]
The verbal phrase line bees is attested from 1827.
1936, network of defensive fortifications built along the northern and eastern borders of France before World War II, in which the French placed unreasonable confidence, named for André Maginot (1877-1932), French Minister of War under several governments in the late 1920s and early 1930s. After the fall of France in 1940, for the next 40 years or so the phrase was associated with a mental attitude of obsessive reliance on defense.