1. The Zoroastrian religious texts state that the mode of disposal of death should have the following four criteria:

(a). The mortal remains of a departed person be taken to an elevated place. (b). It should be as much away from habitation as possible. (c). The corpse should be exposed to carrions (corpse eating birds) like vultures, kites and crows. (d). The corpse should be exposed to the rays of the Sun (khurshed nagirashni)

2. Since ancient times, even before prophet Zarathushtra, the Mazdayasnis used this system of disposal of the dead. Later prophet Zarathushtra too accepted this system and fortified it further. Throughout the Shahnameh there are references of kings desiring to be exposed in the dakhmas, and the Iranian kings giving the benefit of Dokhmenashini even to their adversaries.
3. Since ancient times, Zoroastrians have been vehemently against any other system or mode of disposal of the dead like burning, burying or keeping in water, as each of the other modes not only use up a lot of natural resources, but also pollute one or the other element of nature.
4. The Dakhmas of ancient Iran were not like the Dakhmas that we know of now. In pre-Zoroastrian times, though the four above mentioned criteria were observed, there was no surrounding wall. Gradually a surrounding wall was built.
5. The earliest Dakhmas were very elementary stone structures with a platform inside and a pit in the centre. In Iran, after every few decades, the place of the Dakhma was shifted.
6. The Dakhmas prepared with elaborate rituals that we have in India now, were developed in India when it was realised that it would not be possible to regularly shift the position of Dakhmas.
7. The Dokhmenashini system is the most ecological and nature friendly way of disposing the corpse. Dokhmenashini is essential even from a spiritual point of view, as the spiritual constituents of the body need to be re-united with their natural constituents like air and sunlight.