Two altars were usually set up together, and they are thus found here and there among the ruins, as at Nakhsh-i-Kustem, the necropolis of Persepolis, where a pair of such altars exist; these are cut, each out of a single block, in a rocky mass which rises some thirteen feet above the level of the surrounding plain. They are of cubic form and squat appearance, looking like towers flanked at the four corners by supporting columns which are connected by circular arches; above a narrow moulding rises a crest of somewhat triangular projections; the hearth is hollowed out on the summit of each altar.* * According to Perrot and Chipiez, "it is not impossible that these altars were older than the great buildings of Persepolis, and that they were erected for the old Persian town which Darius raised to the position of capital." At Meshed-i-Murgab, on the site of the ancient Pasargadas, the altars have disappeared, but the basements on which they were erected are still visible, as also the flight of eight steps by which they were approached. Those altars on which burned, a perpetual fire were not left exposed to the open air: they would have run too great a risk of contracting impurities, such as dust borne by the wind, flights of birds, dew, rain, or snow. They were enclosed in slight structures, well protected by walls, and attaining in some cases considerable dimensions, or in pavilion-shaped edifices of stone adorned with columns. [Illustration: 032.jpg THE TWO IRANIAN ALTARS OF MURGAB] Drawn by Boudier, from Plandin and Coste. The sacrificial rites were of long duration, and frequent, and were rendered very complex by interminable manual acts, ceremonial gestures, and incantations. [Illustration: 032b.jpg THE OCCUPATIONS OF ANI IN THE ELYSIAN FIELDS] In cases where the altar was not devoted to maintaining a perpetual fire, it was kindled when necessary with small twigs previously barked and purified, and was subsequently fed with precious woods, preferably cypress or laurel;* care was taken not to quicken the flame by blowing, for the human breath would have desecrated the fire by merely passing over it; death was the punishment for any one who voluntarily committed such a heinous sacrilege. The recognised offering consisted of flowers, bread, fruit, and perfumes, but these were often accompanied, as in all ancient religions, by a bloody sacrifice; the sacrifice of a horse was considered the most efficacious, but an ox, a cow, a sheep, a camel, an ass, or a stag was frequently offered: in certain circumstances, especially when it was desired to conciliate the favour of the god of the underworld, a human victim, probably as a survival of very ancient rites was preferred.** * Pausanias, who witnessed the cult as practised at Hierocaesarsea, remarked the curious colour of the ashes heaped upon the altar.