Fortress Cities
Walls, bastions and citadels still dictate the shape of these towns, and climbing the ramparts remains the best introduction. Fortress cities turn military geometry into some of travel's most theatrical silhouettes.
A fortress city is one whose form was decided by defence and then outlived the threat. What makes these places worth the journey is that military logic produces shapes nothing else would.
The plan is an argument. Palmanova is a nine-pointed star laid out so every bastion covers its neighbours — designed so well that nobody attacked it, and the Venetians had to offer pardoned criminals free land to persuade anyone to live there. Derbent closed the three-kilometre gap between mountain and sea with two walls running into the water.
Survival is usually accidental. Bergamo's walls are intact because Venice never had to use them; Carcassonne was a slum scheduled for demolition until a nineteenth-century theorist restored it, adding roofs scholars still argue about.
Read the failure too. Where the walls were breached, when, and what the besiegers did afterwards is part of the portrait, stated plainly.
Living forts are different. A few — Jaisalmer, Sighișoara, Galle — are still inhabited inside the walls, with the problems that brings: modern plumbing is dissolving Jaisalmer's foundations.
Walk the circuit, and look at where the ground falls away.