Alexi Petrovich visited Dresden in 1709, not 1609, by the way.

Basically "fortification" meant training as a military engineer. It would include study of the architecture and engineering necessary to build what is called today a "star fort" but was called at the time "trace italienne".

Training would probably include:

• A strong focus on drawing and drafting, including both formal architectural drawings and quick field sketches.

• The process of constructing and maintaining forts, including not only design but also logistics -- if you want a fort enclosing so many acres, it will take so long to build in terms of material and man-hours.

• As part of his military education, we would be taught how to use drawings of the exterior of a fort to deduce probable interior structures -- a useful skill for a future military strategist.