The Gemara says that King Hezekiah (Chizkiyahu) closed one of the springs of water in (under?) Jerusalem, so the Assyrian army wouldn't be able to use it. Do we have any guesses what exactly that ...
I have often seen reference to the Four Holy Cities: Jerusalem, Hebron, Safed and Tiberias. What is the earliest source to reference this? Why these four cities? Has there ever been a different count? ...