Duden 108: "According to Mircea Eliade, the sacrum or to hieron is that object in which the transcendent appears. It is a technical term for those things to which the manifestation is tied."
"a sacrum, a material object, will always be found at the center of culture. In, through, or around this object, the culture's hierophany takes place."
"to hieron is neither image nor likeness, neither symbol nor metaphor; it is threshold rather than arrow. It is a frontier at which one can wait, a doorway to the beyond, a window"
"The place or things which roots the appearance of to hieron in the cultural universe is precisely the sacrum"
see Sacred and Profane