Stevin’s Arithmetica (1585) shows the concept of number in the making, and its first systematic definition, as well as of some special extensions. The fourth centenary of its publication is an opportunity to elucidate what characteristic puzzles the resolution of the 3rd degree equations presented, in the form Cardan had attempted it (in 1545), following Tartaglia’ s computations (1539). The paradoxical nature of this puzzle was only overcome as the result of a slow maturing in awareness a lengthy process in which the work of Descartes, later of L’Hôpital and Leibniz, and finally of König (1749) were to be as many significant moments, generally insufficiently known and appreciated.