The present paper discusses the educational potential of reading historical sources in the mathematics classroom under the viewpoint of hermeneutics. In a first step, key concepts of Gadamerian hermeneutics will be discussed, ‘application’, ‘hermeneutic circle’ and ‘prejudice’. Taken in their entirety they characterize what Gadamer calls the ‘historicity of understanding’ which reflects the intellectual situatedness of any reader and provides a foundation to the idea that any text allows a multitude of possible interpretations. In a second step, three readers of ancient Greek texts on astronomy are studied in order to exemplify the functioning of Gadamer’s hermeneutic conception. The readers are students (grade 9), thepedagogue Martin Wagenschein (1896 – 1988) and the philosopher Karl Raimund Popper (1902 – 1994). We show their different intellectual backgrounds, different questions and problems they were interested in and the quite different ways of reading the sources. Nevertheless, there exists an important point of convergence. They all understood the epistemological relevance of their ancient sources culminating in the question of « How is science possible? ». Indeed, this question is and should be a central theme of education.