Societies create order by stigmatizing certain disorderly conditions and events and persons as ‘polluting’, that is, by treating them metaphorically as unclean and dangerous. Very roughly, the pollutions generally recognized by the Greeks were birth, death, to a limited degree sexual activity, homicide except in war, and sacrilege; certain diseases, madness above all, were also sometimes viewed in this way, while mythology abounds in instances of extreme pollutions such as incest, parricide, and cannibalism.Different pollutions worked in different ways (local rules also varied). We get some indication of the attendant casuistry from, above all, a long code from Cyrene (SEG 9. 72) and the rules of purity attached to certain Coan priesthoods (F. Sokolowski, Lois sacrées des cités grecques (1969), nos. 154, 156). To give some illustrations: contact with a dead person of one's own family pollutes for longer than with an unrelated person; a person entering a house of birth becomes polluted, but does not transmit the pollution further; sexual contact only requires purification if it occurs by day…Pollution has a complicated relation to the sacred.