How did high curtain walls protect medieval castles before gunpowder artillery?

Before the advent of gunpowder artillery, high curtain walls served as the primary defense for medieval castles by providing a formidable physical barrier against traditional siege tactics.12

Their protective functions included:

• Frustrating Escalade: By building walls high enough, defenders could prevent attackers from successfully using ladders to scale the fortifications.1
• Providing Defensive Platforms: Unlike wooden palisades, stone walls were fitted with parapets and crenellated firing positions. These allowed archers and crossbowmen to safely engage attackers while remaining protected.1
• Supporting Defensive Features: Walls were often equipped with machicolations—permanent stone galleries—or wooden hoardings. These structures allowed defenders to drop stones, arrows, or boiling substances directly onto the heads of attackers at the base of the wall.13
• Integration with Towers: Walls were typically reinforced by protruding towers, which were often built higher than the wall itself. This design enabled defenders to provide flanking fire along the face and foot of the wall, denying attackers an undisturbed approach for mining or using battering rams.1

These measures made direct assaults extremely difficult, often forcing attackers to rely on treachery, starvation, or disease to overcome the stronghold.1