Emergencies have always been part of city life, but their frequency has changed. Climate instability, cyberattacks, and the interconnected nature of modern infrastructure have pushed events that were once exceptional into something closer to routine. Cities are responding, but the institutions many of them are relying on were designed for a different era. This paper maps how cities organise for emergencies and proposes a new design tool for city leaders. 

The concept of a stack borrows from technology: a stack is a layered architecture where each component has a distinct function, and the whole only performs when the parts connect. Applied to city governance, the stack has five layers: 

• what an emergency system must do
• who carries those functions
• shared standards and protocols
• digital infrastructure
• physical infrastructure.