12I must not omit to speak of the formation of harbours, but explain in what manner ships are secured therein in stormy weather. If they are naturally well situated, and have rocks or long promontories jutting out, which from the shape of the place, form curves or angles, they are of the greatest utility; because, in that case, nothing more is necessary than to construct porticos and arsenals round them, or passages to the markets; and then erect a tower on each side, wherefrom chains may be suspended across by means of machinery.
2But, if the place be not thus fitted by nature, nor secure for ships in stormy weather, and there be no river there to prevent it, but on one side there is a proper shore, then on the other side, by means of building or heaps of stones, a projection is run out, and in this the enclosures of harbours are formed. Building in the sea is thus executed. That powder is procured, which is found in the country between Cumæ and the promontory of Minerva, and is mixed with the water in the proportion of two parts thereof to one of lime.
3Then, in the place selected, dams are formed in the water, of oaken piles tied together with chain pieces, which are driven firmly into the bottom. Between the ranges of piles, below the level of the water, the bed is dug out and levelled, and the work carried up with stones and mortar, compounded as above directed, till the wall fills the vacant space of the dam. If, however, from the violence of the waves and open sea the dams cannot be kept together, then on the edge of the main land, a foundation for a wall is constructed of the greatest possible strength; this foundation is laid horizontally, throughout rather less than half its length; the remainder, which is towards the shore, is made to overhang.
4Then, on the side towards the water, and on the flanks round the foundation, margins, projecting a foot and a half, are brought up to the level already mentioned. The overhanging part is filled up underneath with sand, brought up level with the foundation. On the level bed thus prepared, as large a pier as possible is built, 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 the waves causes the fall of the mass into the sea, and by a repetition of this expedient the work may be carried forward into the sea.
5When the place does not afford the powder named, the following method is to be adopted. Double dams are constructed, well connected with planks and chain pieces, and the cavity between them is filled up with clay and marsh weeds well rammed down. When rammed down and squeezed as close as possible, the water is emptied out with screw pumps or water wheels, and the place is emptied and dried, and the foundations excavated. If the bottom be of loose texture, it must be dug out till a solid bottom is come to, wider than the wall about to be erected, and the wall is then built of stone, lime, and sand.
6But if the bottom be very soft, alder, olive, or oak piles, previously charred, must be driven, and the intervals between them filled with coals, as directed above for the foundations of theatres and walls. The wall is then raised with squared stones, the joints of which are to be as long as possible, in order that the middle stones may be well tied in. The inside of the wall is then filled with rubble or masonry; and on this, even a tower might be erected.
7When this is completed, the arsenals are to be constructed chiefly with a northern aspect; for if they are to the south, the heat will generate and nourish the rot, the worm, the ship worm, and other noxious insects; and timber should be sparingly used in these buildings on account of fire. No rule can be given for the size, but they must be suited to receive the largest ships, so that, if drawn ashore, there may be plenty of room for them. In this book, as far as it has occurred to me, I have treated of the public buildings necessary for the use of a city: in that following, I shall treat of the convenience and symmetry of private houses.