Throughout San Francisco There Are Brick Circles In The Streets. What Are They? San Francisco set brick circles into more than a hundred of its intersections. Cars roll over them every day. Each circle marks the top of a cistern that holds roughly 75,000 gallons and has no connection to the city’s regular water mains. On the morning of 18 April 1906 the earthquake broke the pipes that ran through soft filled ground. Firefighters opened hydrants and got almost nothing. The fires that followed burned for three days and destroyed about 28,000 buildings. The city already owned a handful of older tanks, but they had been left to decay. In 1908 it spent five million dollars on a separate system that included its own reservoir on Twin Peaks, pumps that could pull salt water from the bay, and these independent cisterns buried under the streets so that a broken pipe would not leave the fire department dry again. The brick ring is the only marker. When the hydrants fail, a crew lifts the manhole and drops a hose straight into the tank. The cisterns are still kept full. The circles are the visible edge of the decision the city made after it watched the water stop…