In the age of cannon and gunpowder, mediaeval fortifications became obsolete. Fortifications evolved into much lower structures with ditches and earth ramparts that would absorb and disperse the energy of cannon fire. Walls exposed to direct cannon fire were very vulnerable, so were sunk into ditches fronted by earth slopes. This placed a heavy emphasis on the geometry of the fortification to allow defensive cannonry interlocking fields of fire to cover all approaches to the lower and thus more vulnerable walls.
Unknown artist, Wehranlage: Architektur & Festungsbau & Wehranlage & Bastion & Batterie & Schlachtenordnung & Kanone, copper engraving on paper, 11.2 x 14.9 cm, 1624; source: SLUB / Deutsche Fotothek, signature: 1.B.3237-1, angeb., Creative Commons Namensnennung - Nicht-kommerziell - Weitergabe unter gleichen Bedingungen 4.0 International Lizenz.