Mosaic[2823] pavements were first introduced in the time of Sylla; at all events, there is still in existence a pavement, formed of small segments, which he ordered to be laid down in the Temple of Fortune, at Præneste. Since his time, these mosaics have left the ground for the arched roofs of houses, and they are now made of glass. This, however, is but a recent invention; for there can be no doubt that, when Agrippa ordered the earthenware walls of the hot baths, in the Thermæ which he was building at Rome, to be painted in encaustic, and had the other parts coated with pargetting, he would have had the arches decorated with mosaics in glass, if the use of them had been known; or, at all events, if from the walls of the Theatre of Scaurus, where it figured, as already[2824] stated, glass had by that time come to be used for the arched roofs of apartments. It will be as well, therefore, to give some account, also, of glass. CHAP. 65. (26.)—THE ORIGIN OF GLASS. In Syria there is a region known as Phœnice,[2825] adjoining to Judæa, and enclosing, between the lower ridges of Mount Carmelus, a marshy district known by the name of Cendebia. In this district, it is supposed, rises the river Belus,[2826] which, after a course of five miles, empties itself into the sea near the colony of Ptolemaïs. The tide of this river is sluggish, and the water unwholesome to drink, but held sacred for the observance of certain religious ceremonials. Full of slimy deposits, and very deep, it is only at the reflux of the tide that the river discloses its sands; which, agitated by the waves, separate themselves from their impurities, and so become cleansed. It is generally thought that it is the acridity of the sea-water that has this purgative effect upon the sand, and that without this action no use could be made of it. The shore upon which this sand is gathered is not more than half a mile in extent; and yet, for many ages, this was the only spot that afforded the material for making glass. The story is, that a ship, laden with nitre,[2827] being moored upon this spot, the merchants, while preparing their repast upon the sea-shore, finding no stones at hand for supporting their cauldrons, employed for the purpose some lumps of nitre which they had taken from the vessel. Upon its being subjected to the action of the fire, in combination with the sand of the sea-shore, they beheld transparent streams flowing forth of a liquid hitherto unknown: this, it is said, was the origin of glass.[2828] CHAP. 66.—THE VARIOUS KINDS OF GLASS, AND THE MODE OF MAKING IT.