Fortification wasn't originally limited to engineers. Many early fortification designers were also noted architects, painters, and sculptors, including Leonardo, Michaelangelo, Martini, and Sangallo. In their designs--only in manuscript form--we see the same presentation styles as later designers (i.e., plan and perspective views). For more information see:
Marani, P.C. (1985). Disegni di fortficazioni da Leonardo a Michelangelo. Firenze : Cantini.
Durer was also interested in fortifications. Late in life he wrote Befestigungslehre, a treatise on warfare. Unlike later works specifically on fortification, Durer's work is very text-heavy and uses both plan and perspective views. It is also notable due to Durer's use of profile views, a development is consistent with earlier artisan uses (as evidenced by Villard's sketch book) but is notably absent from the fortification sketches of Leonardo or Michaelangelo.
Dürer, Albrecht (1980). Befestigungslehre. Nördlingen : A. Uhl.