The following is an excerpt from The Watchers Guidebook, pages 11-12:
According to legend, the Watchers were created in the thousand years after the Great Flood, when Ammelatu the Akkadian, a sandalmaker in the city of Agade, witnessed the great Gilgamesh, King of Uruk, come back to life in battle. Ammelatu kept his king's secret safe and, leaving his own life and livelihood, began to follow him. Soon he realized that Gilgamesh was not alone, that there were others like him who could not die, and he began to note who this Immortal encountered and who he killed. As time went on, and more Immortals were made knkown to Ammelatu, he sought out men he could trust and swore them to secrecy, and they began to Watch, as well. On his deathbed, he annointed his three sons men to lead the brotherhood he had created after he was gone, and thus created the first Tribunal.
There are many within the Watcher organization who believe that tale to apocryphal, a fable created during the Dark Ages to explain the unknowable. There is evidence to indicate that the three-person Tribunal only came into being as recently as the Roman epoch. Still, whether the story of Ammelatu is truth or fiction, it illustrates the principles that have been the foundation of the Watchers since its beginning:
This is our Vow, passed down through the ages. These are the principles to which mortal men and women have dedicated their lives for thousands of years. And these are the principles to which you'll swear when you complete your training, take your final vow, and are marked with the seal of the Watchers forever.