When movable-type printing spread across Europe in the late fifteenth century, its most immediate effect was not the diffusion of new ideas but the stabilisation of old ones. Before print, every copy of a text was made by hand, and each copyist introduced errors; important works existed in dozens of quietly divergent versions. Print fixed a text in hundreds of identical copies, which made it possible, for the first time, for scholars in different countries to argue about precisely the same passage. Standardisation, in other words, preceded innovation: only once readers could trust that they shared a common text did the rapid accumulation of criticism, correction and new knowledge that we associate with the print era become possible.