The Latin edition of the Mathematicae Collectiones was published in print in 1588, thirteen years after Federico Commandino’s demise. For his Latin version of Pappus’s work, Comandino used two Greek codices, formerly identified by Treweek. In this article, another Greek manuscript, revised and annotated by Commandino, is revealed. Two letters from Commandino to Ettore Ausonio shed new light on the edition of Pappus’s Collectio and show the partnership between the two mathematicians in elaborating supplementary proofs to include in the comments. (...) Using these letters, we can date the first draft of the Latin version in the late 1560s. The posthumous edition of the Mathematicae Collectiones involved Commandino’s disciples and, in particular, Guidobaldo del Monte. The comparison between the manuscripts and the printed edition reveals an important role played by the disciple in revising the Latin translation of his master. (shrink)