A dakhma, also known as the Tower of Silence, is a circular, raised structure built by Zoroastrians for excarnation – that is, the exposure of dead human bodies to carrion birds, usually vultures.
Zoroastrian exposure of the dead is first attested in the mid-5th century BCE Histories of Herodotus, but the use of towers is first documented in the early 9th century CE. The doctrinal rationale for exposure is to avoid contact with Earth, Water, or Fire, all three of which are considered sacred in the Zoroastrian religion.
One of the earliest literary descriptions of such a building appears in the late 9th-century Epistles of Manushchihr, where the technical term is astodan, „ossuary“. Another technical term that appears in the 9th/10th-century texts of Zoroastrian tradition (the so-called „Pahlavi books“) is dakhmag, for any place for the dead.
The modern-day towers, which are fairly uniform in their construction, have an almost flat roof, with the perimeter being slightly higher than the centre. The roof is divided into three concentric rings: the bodies of men are arranged around the outer ring, women in the second circle, and children in the innermost ring. Once the bones have been bleached by the sun and wind, which can take as long as a year, they are collected in an ossuary pit at the centre of the tower, where – assisted by lime – they gradually disintegrate, and the remaining material – with run-off rainwater – runs through multiple coal and sand filters before being eventually washed out to sea.