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.
2But if we have a situation without natural advantages, and unfit to shelter ships from storms, it is obvious that we must proceed as follows. If there is no river in the neighbourhood, but if there can be a roadstead on one side, then, let the advances be made from the other side by means of walls or embankments, and let the enclosing harbour be thus formed. Walls which are to be under water should be constructed as follows. Take the powder which comes from the country extending from Cumae to the promontory of Minerva, and mix it in the mortar trough in the proportion of two to one.