Ancient Sources

The Jordan Valley

Josephus, War 4.8.3 (1st cent. A.D.)
There is a fountain by Jericho, that runs plentifully, and is very fit for watering the ground: it arises near the old city which Joshua, the son of Nun, the general of the Hebrews, took the first of all the cities of the land of Canaan by right of war (...) it was made gentle, and very wholesome and fruitful, by the prophet Elisha (2 Kings 2:19-22).

BIBLICAL BACKGROUND

2 Kings 2:19-22 "I have made this water wholesome"
Now the people of the city said to Elisha, "The location of this city is good, as my lord sees; but the water is bad, and the land is unfruitful." He said, "Bring me a new bowl, and put salt in it." So they brought it to him. Then he went to the spring of water and threw the salt into it, and said, "Thus says the Lord, I have made this water wholesome; from now on neither death nor miscarriage shall come from it." So the water has been wholesome to this day, according to the word that Elisha spoke.

MORE ANCIENT SOURCES

Itinerarium Burdigalense 596 (333 A.D.)
Eighteen miles from Jerusalem is Jericho. Coming down the mountain range you reach a tomb on the right, and behind it is the sycamore tree which Zaccheus climbed in order that he could see Christ. A mile and half from the city is the spring of the prophet Elisha; at one time any woman who drank from it would never have children.Then Elisha brought a cruse with salt in it, and came and stood over the spring, saying, "Thus saith the Lord, he hath cleansed this waters." Now if a woman drinks from it she will have children.

Anonymus Placentinus, Itinerarium 14 (ca. 570 A.D.)
The spring which Elisha made sweet supplies the water for the whole of Jericho. Grapes grow there for the wine they give to soothe fevers, and also dates which weigh a pound. I brought some back home with me, and gave one to our nobleman, Lord Paterius. A forty-pound citron is a native of the place, and the fruit has a stalk two feet long and two fingersbreadth thick. There is also vine from which baskets-full of grapes are on sale at the time of our Lord's Ascension: and at Pentecost there is wine from it, fo which they are selling great jars.