Although the term synesthesia does not formally make its way into medical discourse until the late nineteenth century, a strong poetic and scientific interest in or desire for synesthetic experiences emerges in the period around 1800 to stage interventions in the era’s dominant philosophical impulses. In German Romantic literature, depictions of synesthetic experiences have significance beyond the mere reveries that the protagonists experience: they prove to be vital lenses through which one can explore and express uncertainty or discomfort with presumed epistemological conditions of the period more broadly and within the role of the literary medium and systems of representation and signification. This dissertation examines depictions of synesthetic experiences in German Romantic literature and thought, and the extent to which they interact with, emulate, or problematize the medial landscape at the time. By looking at these experiences through and in relation to Romantic interarts and intermediality, this project illustrates the different ways in which such experiences also undermine Idealist-inflected conceptions of art and the Absolute, and are imbricated in Romanticism’s crisis of media (Oesterle and Neumann). An analysis of key episodes from the works of Friedrich Schlegel, E.T.A. Hoffmann, Johann Wolfgang von Goethe, and Justinus Kerner reveals both continuities and disjunctions between different clusters of Romantic thinkers and plots a trajectory to rethink the bifurcation between early and late Romantic clusters. Turning to the ways in which each author’s treatment of perception is tied to their poetics reveals an ongoing materialization of perception through the ways each of these thinkers navigates tensions between the visual and the verbal, materialism and idealism, and the spatial and temporal influences on and origins of perception. The opposition of color/light or darkness/shadows visible throughout the works and thought of each thinker highlights on the one hand the ways in which illusions are constructed in the texts, and on the other, draws attention to the limits of perception, an aspiration of both synesthesia and intermediality.