The exact number of poems written by Beltjens is unknown. He didn't have his work published until late in life: in magazines, anthologies and in a few thin, cheaply printed collections.
Beltjens was no innovator. His inner life is close to that of big names in French Romanticism like Lamartine, Hugo and Baudelaire. His early work, like the poem 'Aurora', has a positive attitude. But most of his work is dominated by pessimism, doubts about the existence of God and the point of human existence, and the evil that dominates our world. The romantic longing for a better world that has been lost finds its most complete expression in the poem 'Le Condor captif', in which a Sout-American bird of prey pines away in a Parisian zoo. This poem is viewed as a kind of self-portrait of the poet. Beltjens' enormous control of language is impressive, as it is in his translations into French of the works of German poet Heine.