It is curious that the mid-Victorian period, which saw Britain at the height of its imperial pomp, also witnessed the emergence of a deep insecurity over the status of English as a poetic literary language. Contextualized alongside Matthew Arnold’s break with poetry, this paper will focus on one influential fin de siècle response to this problem in Walter Pater’s historical novel Marius the Epicurean (1885). Set during the Rome of the Antonines, the novel historicizes a series of contemporary anxieties, allowing Pater to muse on the status of English as a literary language through a discussion of the use of Latin as a vernacular language during the age of Marcus Aurelius. The focus in particular will be on the chapters ‘Euphuism’ and ‘A Pagan End’, in which Marius’ friend Flavian constructs his new literary program, asserting ‘the rights of the proletariate of speech’, and writing the (anonymous) Pervigilium Veneris. Contextualising these passages alongside firstly the theme of cosmopolitanism, the utopian dream of the κοσμοπολίτης that frames so much of the novel, both historically and in contemporary fin de siècle discourse, alongside the (here related) discourse of decadence developed in these chapters and in Pater’s essay on ‘Style’ (1888), the paper will conclude by examine Pater’s own English as a kind of vernacular, one at once scholarly, decadent and cosmopolitan, mixing ‘racy Saxon monosyllables […] with those long, savoursome, Latin words, rich in “second intention”’, to consider seriously Mallarmé’s suggestion that Pater was ‘le prosateur ouvragé par excellence de ce temps’.