We dont know when the Cave of Elijah, in Haifa, first became sanctified. We have no ancient references to it. The Crusaders attached Christian significance to it either because of the biblical association of Mt. Carmel with Elijah, or because of a Byzantine tradition that the holy family lodged there on the way from Egypt to Nazareth. Based on his miraculous translation to heaven and on the statement in Malachi 3:23 that
Lo, I will send the prophet Elijah to you before the coming of the awesome, fearful day of the Lord,
Elijah took on a role, in both Christian and Jewish thought, as the messenger who will proclaim the dawn of the messianic age, the precursor of the messiah. Therefore, he was identified by Jesus with John the Baptist (Matthew 11:13-14):
For all the prophets and the law prophesied until John; and if you are willing to accept it, he is Elijah who is to come.
Thus, Mt. Carmel took on special meaning for the Christians, and the Cave of Elijah became holy for them. However, they were not alone, and once the Moslems defeated the Crusaders, they took over the cave, which, it turns out, is holy for them too, as the Cave of El Khader (The Green One). In the Koran, The Sura of the Cave (XVIII), there is a cryptic reference to a runaway fish, to Moses asking for his breakfast, and to Alexander the Great. This seems to be connected to an ancient folk tale of Alexander the Greats search for the fountain of eternal life. Somewhere along the path of his conquests, Alexanders cook was preparing breakfast, drew some water from a local spring, and dropped in a salted fish. When the fish began to swim, the cook realized what he had found, drank a glass of the water, and ran to summon Alexander. But when they came back to the spot, the miraculous spring had disappeared. Alexander, in his frustration, decided to execute the cook which turned out, of course, to be impossible! So he tied a millstone around the cooks neck and threw him into the sea; that is the origin of El Khader, the Green One, who never died and who roams the earth just like our Elijah, testing, helping, rewarding and punishing. And this cave, a stones throw from the sea, is his place, a holy site for Moslems. And like Elijah, El Khader seems to have a special interest in caves, as there are a number of other caves around the Galilee and even down near Bethlehem (where there is a village named El Khader) associated with this popular character.
As control of the Land of Israel passed back and forth between Moslems and Christians, so did the jurisdiction over the cave. Travelers complained about the high admission fees charged to Christians and Jews by the Moslem custodians of the cave. Finally, in 1635 the Christians gave up and found another cave, about a 30 minute hike up the mountain, declared it the Cave of Elijah, and built a church over it, attached to a large Carmelite monastery. This complex (destroyed and rebuilt in the 19th century) is a Haifa landmark today, the Stella Maris monastery. The world-wide Carmelite order has its origins here on Mt. Carmel: there were spiritual seekers among the Crusaders who moved to isolated caves on the slopes of the Carmel, to live lives in imitation of Elijah. Ultimately, some of these hermits requested recognition as a religious order, and received it in 1209.
So now there are two caves of Elijah (at least), and many caves of El Khader. In this rocky soil, holiness spreads like a weed