They seem to have been deliberately selected and placed at specific points in the circle that mark certain calendrical events (sunsets and solstices related to the four seasons, for example).
en.wikipedia.org Whenever excrescences are encountered, an initiating and an exorcising amulet are placed over them, then they can no longer conceal or transform themselves.
en.wikipedia.org Clean-outs should be placed in accessible locations at regular intervals throughout a drainage system, often including outside the building, because clean-out augers have limited length.
en.wikipedia.org Ultimately, however, he feels his overseas experience and interest have placed him in a part of the oil patch that is uniquely positioned for growth.
www.theglobeandmail.com Emphasis shall be placed on self-discipline, self-reliance, personal responsibility, and accountability.
en.wikipedia.org