One of the ancient aqueducts that supplied the city, at its peak the Acquedotto Claudia was able to provide all 14 districts with water. The hugely relied upon source inexplicably went dry for nine years right around the time Nero was building his modest Golden Palace. His little pet project required vast amounts of water, but, luckily, the main build site was at the foot of Claudia's castellum (or storage reservoir). When the palace was completed the water conveniently came back. To this day historians are baffled as to what caused the drought. My bet: dramatic tension.