In Flanders fields the poppies blow
Between the crosses, row on row,
That mark our place and in the sky,
The larks, still bravely singing, fly,
The poem begins by invoking the poppies, which have since come to be the symbol of the fallen in the First World War and in subsequent wars. Apart from growing spontaneously on disturbed ground where trenches were dug and then around the graves of buried dead, the red petals and black heart of the flower represent life and death. 
 The cemetery referred to is located in Flanders, Belgium. The Flanders region was the site of the bloody Second Battle of Ypres, at which McCrae fought with the Canadian army. A combined total of over  105,000 soldiers  were killed or wounded in the battle. 
 
 President Obama during a  wreath-laying ceremony at Flanders Fields Cemetery on March 26, 2014 
 Poppies produce a powerful narcotic–they are the source of opium–and are often associated in poetry with sleep and death (the eternal sleep). In this context they are associated with fallen soldiers. 
 
 This Canadian stamp containing the first lines of the poem was issued in 1968 to commemorate 50 years since McCrae’s death.