Instruction on the Fortification of Cities

A geometric diagram illustrates the principles of perspective. A central vertical line extends from a decorative point at the top, passing through point "α" and ending at point "h" on a horizontal baseline labeled "d-h-e". A large triangle is delineated by lines connecting the top point to points "d" and "e". Within this triangle, an intermediate horizontal line is marked with points "δ", "b", and "ε". Several diagonal lines extend from the baseline, converging toward the top point and creating a grid-like perspective on the ground. Additional perspective lines on the left and right suggest depth. Faint outlines of architectural windows are visible in the background, likely bleed-through from the other side of the page.