The Gihon Spring

You would expect Jerusalem to be a dry city. With no river and very little rainfall how has it survived as a vital urban center for more than three millennia?

Since ancient times, Jerusalem has relied on two natural springs: En-Rogel in the Kidron Valley on the south side of the city, and the more important one, the Gihon spring on the east side of the hill of Jerusalem. The Gihon is a karst spring fed by groundwater that accumulates in a subterranean cave; whenever the space fills to the brim, it empties through cracks in the rock and is siphoned to the surface. But that surface is still well below the level of the city.