How is mathematical knowledge recorded and preserved across generations? Contrary to the idea that mathematics itself is somehow ‘permanent’, in this talk we will explore heritage-making in mathematics, that is the people, institutions, and material objects that can give mathematical ideas longevity. We will explore the heritage-making found in two very different types of French nineteenth-century libraries: those of famous mathematicians and those of secondary schools. We will especially focus on how the recording – and forgetting – of mathematical ideas is influenced by their publishing, political, and intellectual contexts. This lecture was recorded by Professor Caroline Ehrhardt on 8th October 2025 at Barnard’s Inn Hall, London.