What is some information on Longinus as a Classic or Romantic critic?
Longinus wrote in the Classic Greek period. Longinus cannot be properly identified. It is thought he was actually a Greek master of rhetoric, though, for simplicity, the writer is consistently called Longinus.
During the Classic period, Longinus had no appreciable impact or influence. This is said to be true because he is not referenced in any other known Classic Greek works, neither is he nor The Sublime mentioned in the Medieval period.
Longinus appears most significantly in 1554 when The Sublime is printed with editing done by Francesco Robortelli. After this and up until 1694, there were seven more printings, including five translations to Latin or French. In the 1700s Longinus became quite popular as did critcism of his critical approach as he detailed it in The Sublime.
While Milton and John Dryden gave Longinus attention in the 1700s, it was Pope, just prior to the Romantic period, that brought Longinus forward with great impact. The Romantics developed partly as a reaction against the poetic standards of Pope and Johnson, thus Longinus's association with them (Pope wrote of him in two works, Essay on Criticism, 1711, and Bathous: Or, The Art of Sinking in Poetry, 1727) may have influenced the Romantics' rejection of his principles, which actually accorded well with the tenets of Romanticism
Longinus theorized that the art and the artist were unified through the artist's character (virtue, vice)--which is reminiscent of the Aristotelian idea of mimesis (imitation) of higher truths poets are inspired to communicate--and that art is the reconciliation of opposites or the unification of antitheses in art (Deconstructions would later give Longinus serious attention in relation to the oppositional binaries so important to Deconstructionism and Modernist theory).
While the Romantics rejected Longinus for being part of Grreek Classicalism, the above two elements of his theory resonated with Romanticism's ideas of inspiration through imagination (tying the artist to his art) and with the importance of elevating common pastoral life and language over sophisticated urban life and language (evidence of Longinus' antithetical opposition and of Deconstruction's later binary opposition).
[For further details, see the eNotes resource links below.]