THE CRIMSON THREAD AT THE TEMPLE

In the Talmud Yoma 67a, it says:

Our Rabbis taught: In the beginning they would tie the thread of crimson wool on the entrance of the Ulam (The Hall leading to the interior of the Temple) without: if it became white they rejoiced; if it did not become white, they were sad and ashamed. Thereupon they arranged to tie it to the entrance of the Ulam within. But they were still peeping through and if it became white, they rejoiced, whereas, if it did not become white, they grew sad and ashamed. Thereupon they arranged to tie one half to the rock and the other half between its horns.