"Pan Tadeusz" (published 1834), another of his masterpieces, is an epic poem that draws a picture of the Grand Duchy of Lithuania on the eve of Napoleon's 1812 invasion of Russia. It is written entirely in thirteen-syllable couplets. Originally intended as an apolitical idyll, it became, as Miłosz writes, "something unique in world literature, and the problem of how to classify it has remained the crux of a constant quarrel among scholars"; it "has been called 'the last epos' in world literature". "Pan Tadeusz" was not highly regarded by contemporaries, nor by Mickiewicz himself, but in time it won acclaim as "the highest achievement in all Polish literature."