HYPAETHRUS, an architectural term used by Vitruvius for an opening in the roof to admit light. Alternative forms are hypaethros and hypaethrum. Many students of Greek temples, especially James Fergusson and T. J. Hittorff, basing their con clusions upon the Vitruvian reference to such an hypaethrus in the temple of Zeus Olympius at Athens, and upon coping tiles found in the temple at Aegina, have concluded that all Greek temples had some such method of admitting light. Moreover, late Greek tombs at Cyrene and Delos show raised copings in the centre of the roof as though for such an opening. And according to Strabo (c. 5o B.c.), the temple of Apollo Didymaeus at Miletus (second half of 4th century B.c.) had its entire vast cella open to the sky and planted with groves of laurel. Pausanias, however, states that this temple was never completed ; if this is so a roof may have been planned originally.
The consensus of modern opinion is counter to the idea that the hypaethrus was a common feature. No arrangements for drainage have been found in connection with Greek temples, and the very reference of Vitruvius on which the speculations of Fergusson, Hittorff and others are based seems to point to the arrangement as exceptional enough to warrant mention, and used only in the largest buildings. Thus the ordinary temple would be lighted only by the enormous doorway; certainly light thus obtained would furnish a more beautiful and impressive illumina tion than any direct glare from above. (T. F. H.)