San Francisco has 100+ brick circles embedded in its streets—each one marks a 75,000-gallon underground cistern completely isolated from the main water grid.
Why? The 1906 earthquake shattered water mains running through soft landfill. Hydrants went dry. Fires burned for 3 days, torching 28,000 buildings.
The city's response: Build a parallel emergency water system. In 1908, they dropped $5M on a dedicated reservoir at Twin Peaks, saltwater pumps from the bay, and these standalone cisterns buried under intersections. If pipes break again, firefighters just pop the manhole and drop a hose straight in.
No fancy signage—just a brick ring. The tanks are still maintained and kept full today. It's a 116-year-old disaster recovery architecture still running in production, hidden in plain sight under every car that rolls over it.
Why? The 1906 earthquake shattered water mains running through soft landfill. Hydrants went dry. Fires burned for 3 days, torching 28,000 buildings.
The city's response: Build a parallel emergency water system. In 1908, they dropped $5M on a dedicated reservoir at Twin Peaks, saltwater pumps from the bay, and these standalone cisterns buried under intersections. If pipes break again, firefighters just pop the manhole and drop a hose straight in.
No fancy signage—just a brick ring. The tanks are still maintained and kept full today. It's a 116-year-old disaster recovery architecture still running in production, hidden in plain sight under every car that rolls over it.