I understand that there is a general Jewish tradition that the Western Wall/Kotel was built by the poor (I believe under the command of King Solomon) [(link)][1]. What is the source for the tradition (being built by the poor, but also when it was built)? All archeology has uncovered is that it was built after the year 20 CE [(link)][2].


> **2) Eternal Symbol**
> 
> The Sages prophesied that even after the Temple's
> destruction, the Divine Presence would never leave the Western Wall,
> and that the Wall will never be destroyed. The Wall is endowed with
> everlasting sanctity, as the Talmud says: "And I will make your
> sanctuaries desolate" (Leviticus 26:31) – this means that the
> sanctuaries retain their sanctity even when they are desolate.
>
> Jerusalem was destroyed and rebuilt nine times. And through it all,
> one symbol remained intact: the Western Wall.
> 
> **5) Built with Love and Dedication**
> 
> When the Temple was being built, the
> work was divided among different sectors of the population. The
> building of the Western Wall fell to the poor, and they worked hard to
> construct it, as they could not afford to hire laborers to do their
> work for them.
> 
> When the enemy destroyed the Temple, the angels
> descended from on high and – spreading their wings over the Wall –
> said: "This Wall, the work of the poor, shall never be destroyed."
> (from "Legends of the Land of Israel")


  

[1]: http://www.aish.com/w/a/46804772.html
  [2]: http://www.nbcnews.com/id/45419597/ns/technology_and_science-science/t/coin-discovery-sheds-new-light-sacred-jerusalem-site/