“From the start of the sanctification of the Western Wall, in the 16th century, the traditions in the texts of the Sages were transferred from the western wall of the Temple [itself] to the western [retaining] wall of the Temple Mount.”
Ofer Aderet has a fascinating article in Ha'aretz about the surprising history of the Kotel (Western Wall). What's so surprising? The Kotel is not as holy as you think. Why? For one thing, it was not a site of worship until the late 1500s.
Here's an excerpt that explains that history:
…The first testimony to the transformation of the Western Wall into a sacred site for worship comes only from the 16th century. “It is known that in the past sanctity was not attributed to the Wall, and the [early] written sources and writings left by Jewish visitors in the Middle Ages testify that the Western Wall was no more important than the other walls of the Temple Mount,” according to Dr. Gabriel Barkay, a professor of archaeology at Bar-Ilan University, in an article in the journal Ariel in July 2007.
The Wall, he wrote, became a holy site only in the early modern period. “From the start of the sanctification of the Western Wall, in the 16th century, the traditions in the texts of the Sages were transferred from the western wall of the Temple to the western wall of the Temple Mount,” explained Barkay. Early evidence of this can be found as we get closer to the 17th century. One such testimony is a letter from the year 1625, in which a traveler from the city of Carpi in northern Italy describes his visit to the Wall in the following words: “I kissed it and prostrated myself at its feet and recited an orderly prayer.”
The development of the Western Wall as a site for worship during the past 100 years is connected to the building of the adjacent Jewish neighborhood − the Old City’s Jewish Quarter − and with the fact that this was the piece of the Temple Mount’s retaining wall that was closest to it. Jewish Quarter residents had convenient access to it, whereas other parts of the wall were inaccessible or even outside the city limits, explained Barkay.
“Apparently, after the Jewish neighborhood moved into the Jewish Quarter of today, Jews began going to the small, exposed segment of the Western Wall for individual prayer, after the public prayers. This custom developed slowly during the course of the 16th century,” wrote Prof. Dan Bahat, the archaeologist who excavated the Western Wall tunnels, in another article in April.
After the earthquake that struck Jerusalem in 1546 and toppled buildings that had stood against the Wall in the worship compound of today, Jews were able to move from the modest area that had served them until then to the prayer site we know today, wrote Bahat. Another reason for the sanctification of the Wall in the past 100 years has to do with the fact that the Western Wall we know today, which was part of the external wall surrounding the Temple compound, was also the closest to the rear wall of the focal point of sacredness in the Temple, the Holy of Holies. That wall, too, was known as the “Western Wall” in early sources. Thus it is easy to link the two walls and their sanctity.
The custom today of placing notes among the stones of the Wall apparently was imported from Europe in the 19th century. Special scribes would help those who needed to write their notes in Hebrew, and then they were placed in the cracks between the stones. At regular intervals, the notes would be removed, gathered in a sack and buried in synagogue genizahs.…
[S]tarting in the early Middle Ages, pilgrims would write their names on the stones of the wall alongside short blessings. Others would rub their hands in paint and make palm prints on the Wall, or engrave their names in the stones with a penknife or a blade. There were also many who drove nails into the wall as a sort of good-luck ritual before traveling abroad.
“In pictures from the end of the 19th century and the early 20th century, the Wall appears to be decorated with inscriptions ... nearly every place a human hand could reach,” wrote historian Dr. Yair Wallach in an article entitled “The Hebrew Inscriptions on the Stones of the Western Wall.”
In the 20th century, protests against the defacing of the wall began to be heard. “Blasphemy unparalleled anywhere in the world,” wrote historian Joseph Klausner, who visited the Wall during his journey to the Land of Israel in 1912. In 1931 the custom of writing on the Wall ceased. According to a law drawn up by the British, “It shall be held to be a matter of common interest to Moslems and Jews alike that the Western Wall should not be disfigured by having any engravings or inscriptions placed upon it or by having nails or similar objects driven into it.”…