As suggested in the title «la militare Architettura» the author Pietro Ruggiero shares his experience building Fortresses and also different war tactics.
Pietro Ruggiero/Pierre Rougier was a Burgundian Frenchman who settled in Milan with a history as mercenary.
The books complete title translates to: Military architecture, a modern fortification, caused by experience, and by various more practicable ways: with the main rules of arithmetic, and doctrine of triangles pertaining to art, conquest, and guarding of squares, and a treatise on military art.
Ruggiero addresses the basic rules for surveying and constructing fortifications, as well as fortress defense and general military tactics. He discusses how the immediate location of a fortress influences how it is supposed to be built. He frequently illustrates his ideas in the book with drawings. The illustrations include fortress plans, diagrams of encampments and architectural details of rampart angles.
Speaking from his own experiences Ruggiero explains different scenarios and lines of attack, many of which were taken from real battles and discusses the logistical problems of war such as supplying fortresses under siege.
In my opinion the book is highly interesting for its historical value and sheer amount of information it entails. The book is extremely extensive and must have, aside from taking a long time to complete, cost a fortune.
However, I believe that the architecture he is documenting in his book has changed so much over the years that there is little we can apply to modern military architecture.