Frontinus is best known as a writer on water engineering, but he had a distinguished military career. In Stratagems he draws partly on his own experience as a general in Germany under Domitian. However, most of the (more than five hundred) examples which he gives are less recent, and similarities to versions in other Roman authors like Valerius Maximus and Livy suggest that he drew mainly on literary sources. The work consists of four books, of which three are undoubtedly by Frontinus. The authenticity of the fourth book has been challenged.