But the winter of 1909-10 was wetter than normal. Heavy rains and melting snow had engorged the soil, and a low pressure system stalled across the English Channel bringing more storms. The previous summer had been particularly rainy raising the water table higher than in recent memory.
When Parisians woke up on January 22, they realized just how far the Seine had shot up. An enormous volume of water was pulsing through the network of underground tunnels--subway conduits, sewer channels, wells, reservoirs, a labyrinth of old quarries from which men had carried stones in previous centuries to build the aboveground city, and basements and crypts dating back to Roman times. The swell of water grew hour by hour as runoff from the streets roared beneath the city, pushing into every nook and cranny. To everyone's surprise, the water was not coming over the high quay walls, but under them.