Pietro Monte and Leonardo Da Vinci lived in Milan at about the same time around 1495 and from a note in the Codex Atlanticus, one can deduce the familiarity of the two Tuscans. This paper tries to explore the nature of the collaboration between the Condottiere who died at Agnadello and the famous inventor in terms of weaponry and tactics. They were both involved in inventing a latin vocabulary to write about the subject and shared thougts about landsknechten’s techniques. It also seems that a lost leonardian treatise quoted by some authors was in close relation with Pietro Monte’s writings in its Collectanea. If we add to these remarks the fact that Leonardo and Monte were both studying internal and external ballistics in practical and philosophical terms, it might be the case that such a collaboration has to be completely reassessed in the future.