to be like onyx marble or crystalline limestone. In Syria the hardest stones possible are selected for the purpose and are heated along with cow dung so that the burning may be accelerated. However, it has been discovered that the best kind is prepared from specular stone^a or from stone that flakes in the same way. Gypsum, when moistened, should be used instantly, since it coheres with great rapidity. However, there is nothing to prevent it from being pounded and reduced again to a fine powder. Gypsum is a serviceable whitewash and is used with pleasing effect for making moulded figures and festoons^b in architecture. A famous story carries with it something of a warning: we are told that Caius Proculeius, a man who could rest assured of his close friendship with the Emperor Augustus, committed suicide by swallowing gypsum when he was suffering from severe pains in the stomach.

LX. Paved floors^c originated among the GreeksPaved floors. and were skilfully embellished with a kind of paintwork until this was superseded by mosaics. In this latter field the most famous exponent was Sosus, who at Pergamum laid the floor of what is known in Greek as ‘the Unswept Room’ because, by means of small cubes tinted in various shades, he represented on the floor refuse from the dinner table and other sweepings, malting them appear as if they had been left there. A remarkable detail in the picture is a dove, which is drinking and casts the shadow of its head on the water, while others are sunning and preening themselves on the brim of a large drinking vessel.

LXI. The original paved floors, in my belief, were