Named for Yazdegird I, the city was, and is, a Zoroastrian centre. It became a haven for Zoroastrian refugees after the Arab conquest, and it still has the largest number of Zoroastrians in Iran. A fire-temple contains a fire that's been alight since AD 470. The practice of exposure of bodies to be recycled by birds seems to have been unwittingly described by Herodotus - but the first "Tower of Silence" is no earlier than the 9th century AD. Ritual exposure was outlawed in Iran in 1970, although it survives (just) among Parsi communities in India. It is a hygienic as well as "green" method of disposal - as vultures' digestive systems contain an enzyme which destroys bacteria. Severe problems have been caused in India as a result of the decline in vultures (due to diclofenac poisoning from eating dead cattle). Dogs spread disease and attract leopards into populated centres - human fatalities have resulted.
Yazd relies on qanats for much of its water supply, as do hundreds of towns and villages in Iran.