Why did European walls evolve triangular star-shaped bastions?

Answer: To eliminate dead zones — each face covers the others

To eliminate dead zones — each face covers the others ✓ — Correct! After 1500, cannons made tall flat walls vulnerable. The fix was geometric: triangular bastions sticking out from the wall, arranged so EVERY face of the fort can be shot at from another bastion. No matter where attackers approach, defenders hit them from the side. This 'trace italienne' design dominated Europe for 300 years and gave us star-shaped fortresses like Naarden and Palmanova.

To deflect cannonballs with sloped angles — Wrong. Sloped walls (glacis) DID help against cannons, but bastions are about flanking-fire geometry, not deflection. The star shape eliminates blind spots — that's its core innovation.

To make the fort visible from a longer distance — Wrong. Bastions actually make a fort harder to spot at distance because the silhouette is broken up. Visibility was never the point — covering every approach with crossfire was.