Wieland’s first novel, Die Abenteuer des Don Sylvio von Rosalva, makes its reflection on fiction and on the marvellous clear; its subtitle (“eine Geschichte, worin alles Wunderbare natürlich zugeht”) and its plot (the adventures and recovery of a new Don Quixote whose mind has been confused by fairy tales) both immediately suggesting a critical perspective. To understand the latter, this paper proposes to examine the conception of relationship between fiction and truth in a diachronic perspective and relates Wieland’s work to the integration of the marvellous into mimesis in the various poetological strategies debated in Germany in the early 18th century. In this light, Die Abenteuer des Don Sylvio von Rosalva emerges as an experimentation of the categories previously discussed in a context renewed by empiricism, thereby redefining the power of fiction and the marvellous.