Kevin Huang | How a Fortress Actually Worked (Castel Sant'Angelo, Rome)

Films show you castles as backdrops. Walking through one shows you a machine for solving problems.

Inside Castel Sant'Angelo the logic is legible everywhere once you start looking for it. A helical ramp climbs from the base through the body of Hadrian's mausoleum — built for a funeral procession, later just as useful for moving defenders and supplies upward. The corridors narrow and turn where an attacker would be most exposed. Rooms are stacked by function: storage low, garrison in the middle, papal apartments and terrace above. On display are the arms and armour of the people who held it, which is the part that makes the abstraction concrete — someone stood in this passage, in that equipment, for a shift.

The thing I had not appreciated before was that a fortress is also a residence. People lived here for centuries: cooking, sleeping, storing grain against a siege that might not come for a decade. The defensive design and the domestic design are the same design. That is a genuinely different mental model from the one I arrived with, which was essentially a castle as a large wall with people behind it.

This was February 2018 and my first time in Europe. I went in expecting spectacle and came out more interested in the constraints — what the builders were afraid of, and what they were willing to spend to be less afraid of it.

I have deliberately not described everything. Half the pleasure is the ramp turning a corner and opening onto something you did not expect, and that does not survive being summarised. Go and find the rest yourself.

Castel Sant'Angelo is on Lungotevere Castello, a short walk from St Peter's along the Passetto's line.

— Kevin Huang (黃冠融 / Guan Rong Huang), Metablox.co