124

pended across by means of machinery. But, if theplace be not thus fitted by nature, nor secure forships in stormy weather, and there be no river there toprevent it, but on one side there, is a proper shore, thenon the other side, by means of building or heaps ofstones, a projection is run out, and in this the enclosuresof harbours are formed. Building in the sea is thusexecuted. That powder is procured, which is found inthe country between Cumee and the promontory ofMinerva, and is mixed with the water in the propor-tion of two parts thereof to one of lime. Then, in theplace selected, dams are formed in the water, of oakenpiles tied together with chain pieces, which are drivenfirmly into the bottom. Between the ranges of piles,below the level of the water, the bed is dug out andlevelled, and the work carried up with stones andmortar, compounded as above directed, till the wall fillsthe vacant space of the dam. If, however, from theviolence of the waves and open sea the dams cannot bekept together, then on the edge of the main land, afoundation for a wall is constructed of the greatestpossible strength ; this foundation is laid horizontallythroughout, rather less than half its length; the re-mainder, which is towards the shore, is made to over-hang. Then, on the side towards the water, and on theflanks round the foundation, margins, projecting a footand a half, are brought up to the level already men-tioned. The overhanging part is filled up underneathwith sand, brought up level with the foundation. On thelevel bed thus prepared, as large a pier as possible isbuilt, which must remain for at least two months to set.The margin which incloses the sand is then removed,and the sand being washed away by the action of thewaves causes the fall of the mass into the sea, and by arepetition of this expedient the work may be carriedforward into the sea. When the place does not affordthe powder named, the following method is to be adopted.