The depth of water in the harbour varies constantly, according to the winds which prevail in the offing. We observed that the greatest increase was with north-westerly gales, and vice versâ; they generally occasioned a rise of two or three feet, and if continued, even more than that. North-easterly winds had but little effect upon it.
REMARKS ON THE NAVAL AFFAIRS OF THE ANCIENTS, AND THE RATES OF SAILING OF THEIR VESSELS AT DIFFERENT PERIODS.
The Greater Syrtis appears to have been at all times ill provided with ports and harbours, and may at the present day be considered to be wholly unprovided with any; that is to say, with any which could be used as such by ships of modern construction. It will be observed that the whole line of coast laid down in the chart is, at the same time, very indifferently formed by nature to afford security to vessels of any description.
It was not, however, necessary that the ports of the ancients should possess wholly by nature those local advantages which are at the present day considered to be essential for affording protection; and we find that many of them existed in places which must always have been unqualified by their position for affording the security required. In such places art was made to supply the deficiencies of nature, and harbours were built where none could otherwise have been obtained. The mode of constructing these artificial ports has been clearly defined by Vitruvius; and as it may serve to explain what we have stated with respect to the present state of the ports of Ptolemeta and Aspis, we shall submit the passage in question as we have extracted it from Wilkins’s translation.
“A spot was, if possible, selected, which had the advantage of some protection on one of its sides; and the want of a corresponding defence on the other side was supplied in the following manner:—rows of grooved beams were driven in the water, connected by oaken planks, and bound together by chains. The surface of the ground below the water was then levelled and consolidated by means of transtilli, and the space comprehended between the beams filled up with a composition of rough stone, and cement formed of sea-sand mixed with lime, in the proportion of two parts to one, which soon produced a solid wall.” The author adds, “that sand should be procured for this purpose from the sea-coast between Cumæ and the promontory of Minerva,” which seems to be considered by him as most efficient in forming the cement here alluded to.
If the beams could not, however, be firmly fixed, on account of the action of tides or currents, or from being too much exposed to a heavy swell from the open sea, a strong buttress is recommended by Vitruvius to be built upon the water’s edge, and a portion somewhat less than half the upper surface of the buttress to be constructed upon a horizontal level, the remaining part inclining towards the sea. Upon the edges of this part of the buttress walls were to be raised to the height of the level part, of a foot and a half in thickness, and the intermediate space filled with sand. Upon this foundation a solid pile, we are told, may be built, which, after being finished, should be left to dry for two months at least. The walls which were raised upon the edges of the inclined surface of the buttress, and which seemed to confine the sand, should then be destroyed; and the water, in washing away the sand by degrees, will undermine the pile, and cause it to be precipitated into the sea. This operation should be repeated until the whole is complete.
In places, however, (Vitruvius observes) where this sand is not to be procured, other methods must be resorted to. The space, which the mole is intended to occupy, having been inclosed by a double range of beams connected by planks and chains, the interval between the ranges should be filled with loam, rammed into baskets made of the ulva palustris. The space being filled by masses of this kind, stowed as closely together as possible, the water contained in the inclosed area may be removed by engines calculated for the purpose, such as cochleæ, rotæ, and tympana; and when the ground is left perfectly dry, the foundations may be dug of greater width than the walls they are intended to support, and filled in with rough stone, lime, and sand. Piles of charred alder, olive, or oak, must first be driven into the ground if it be soft, and the intervals between them filled with charred wood, in the manner recommended for forming the foundations of the walls of theatres. The walls should then be built upon these foundations with squared blocks of considerable length, so that the stones between these blocks, which extend across the wall, may be bound firmly together. The space inclosed by the walls may be filled in with rubble, or stone-work, and be made so firm that a tower may be erected upon it. The mole being completed, (continues our author) the docks should be built facing the north; because the greater heat of a southern aspect occasions a more rapid decay, and engenders and nourishes moths, ship-worms, and other noxious insects. Timber should, at the same time, be used as sparingly as possible in works of this kind, that they may not be liable to accidents by fire[9].
Harbours[10] of this kind were usually built in a semicircular form, with arms of great length extended into the sea; these were sometimes called χηλαι, from their resemblance to crabs’ claws[11]; Cicero terms them cornua (horns). (Epist. ad Attic. lib. ix. ep. 19.)
For the better security of the ships within the harbour, it was usual to draw strong chains or booms across the entrance, and to defend them with large pales, fortified against the water with pitch. On both sides of the mole were strong towers, which were garrisoned with troops; and not far from these was a watch-tower, or lighthouse, called Pharos, which name belonged originally to a little island in the mouth of the Nile, where the first of these towers was built, but was afterwards naturalized both in Greece and at Rome. In the innermost part of the harbour vessels were often suffered to lie unmoored, whereas in other parts of the port, which were not so well secured, they were either chained to the land, or obliged to lie at anchor. This portion of the harbour was divided into several partitions by walls, constructed for the most part with stone, within which the vessels laid very securely, without the necessity, as we have just mentioned, of using either cable or chain. These places were termed ορμοι, υφορμοι, ναυλοχοι, ormoi, uphormoi, naulokoi, &c., and formed altogether what was called ναυσταθμος (naustathmos[12]).
Here were likewise the docks in which ships were built, or careened, drawn up on the beach.