IR47. 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



31 



an extensive scale, conlainingr all the requisites for carrying on a co-isiil'r- 

 able tiadf for ihe supply of Rome, and for the construction and mainten- 

 ance of llie fleets, which were stationed in this quarter for the proleclion 

 of the capital, as well as for the purpose of sending expeditions to the 

 various departments of the widely extended Roman Empire. The whole 

 of the harbour was surrounded by an extensive and lofty fortified wall, 

 flanked with towers, quite independent of Ihe town of Ostia, which was 

 alsn surrounded by a wall. 



Old Port filled up. — The port of Claudius Caesar has now become com- 

 pletely filled up by the alluvial matter brought in by the littoral currents, 

 as well as by the deposit of the Tiber, and is now aboul a mile from the 

 shore. We cannot be surprised at this result, but at the same time we 

 nnist admire the great skill ingenuity, and perseverance by which it was 

 attempted at that early period, to overcome by means of art the obstacles 

 interposed by nature. 



Dred'^ini; — It is a question well worthy of serious consideration how 

 far this principle may be carried with advantage, or where the obstacles 

 interposed by natural causes become too powerful for the comparatively 

 feeble resources of art. The Clyde at Glasgow, and the Lilfey at Dublin, 

 are extraordinary examples of what may be effected by this system. The 

 harbours also of Boulogne, Calais, Duukerque, and Osteud have all been 

 materially improved in this manner; it still, however, remains to be proved 

 how much further this system can be carried with advantage at these ports. 

 It is doubtful whether the ancients were acquainted with, or had applied 

 tlie modern system of penning up water in large reservoirs, and then dis- 

 diarging it with increased velocity by means of sluices, so as to enable it 

 to act with more effect in scouring and deepening navigable channels : it 

 most, however, be recollected that this system can only be practised with 

 advantage when there is a considerable rise of tide (which docs not take 

 place in the Mediterranean), for otherwise it is diflicult to obtain sufficient 

 head or fall to discharge the water from the reservoirs with tlie required 

 Telocity. 



In the second place, as regards the harbour of Claudius, there was 

 dearly a great effect, accompanied by considerable boldness, as well as 

 ingenuity, both in the design and execution. He must have foreseen, 

 judging from past experience, that it was in vain to contend farther with 

 the difficulties of the Tiber, and determined at once to get rid of them by 

 making an entirely new harbour, which he anticipated would be entirely 

 free from similar objections, and yet, at the same time, would be sufficiently 

 near to communicate with the Tiber, and to take advantage of its naviga- 

 tion to Kome. The works were designed and constructed upon a magnifi- 

 cent scale, comprising almost every principle, both in design and construc- 

 tion, adopted at the present time, with the exception of the open or arched 

 mole, which was peculiar to the ancients. This principle is certainly in- 

 genious, and is well designed to obviate one of the most serious difficulties 

 in maintaining a harbour upon a flat alluvial coast like that of Ostia. It 

 might be applied with advantage to many cases in modern times, and it is 

 singular that it has not beeu more studied, although it must be admitted, 

 that the great rise of tide and the stormy nature of the northern seas (eir- 

 ctimslances which do not exist in the Mediterranean) interpose practical 

 diflicullies in carrying the system into efiect. It has been tried with ad- 

 vantage upon a small scale in the outer harbour of Ramsgate, and there 

 are many cases where it might prove equally applicable. The double eu- 

 trance, when circumstances admit of its being tried, is very valuable, and 

 where it cannot be used, such a particular form of entrance is desirable 

 as would enable vessels under sail to enter and depart at all times ; and at 

 the same time would prevent too great an increase of sea. Such a princi- 

 ple was adopted by the late Mr. Rennie at Uonaghadee, and was also 

 proposed by hini at Kingstown. 



The curved form of the ouler piers, although well calculated to facililale 

 the passage of the current, was ill adapted to break the waves; ou lii., 

 contrary, it tended rather to increase their force, particularly at the en- 

 trance, where tranquility was much required : the angular form would 

 therefore have answered this purpose better. 



Construciion.—As. regards construction in Ostia, there is an illustration of 

 almost every principle in use at the present time ; the rubble thrown pro- 

 miscuously into the sea to form its own slope, according lo specific gravity 

 of the materials and the action of the waves upon them ; the solid vertical 

 wall ot masonry with arches resting upon piers, founded by means of 

 pozzulano and rubble mixed in caissons; and the caisson and piled 

 foundalion for the light-house on the outer detached mole. There is no 

 account of the diviug-bell having beeu applied to the purpose of building 

 underwater, but the use of the material pozzolano, which abounds in Italy 

 was well uoderstuod and generally adopted. The mode employed in using 

 It was to mix the pozzolano in a moist state with certain proportions of 

 hme and small pieces of stone, then to throw the whole mass into a dam or 

 caisson. construc(ed in Ihe form required, and there to leave it until it had 

 set sufficiently hard ; the caisson might then be removed, and the mass of 

 concrete left standing, and which became more solid the longer it remained 

 as the ruins of Caligula's Bridge bear ample testimony. The same system' 

 IS pursued in many of Ihe ports of Italy at the present day. The French 

 at their new moles at Algiers and Cherbourg, are said to have extended 

 this system with advantage; yet its meriis, as compared with masses of 

 natural stone, still require the test of time to prove its superiority.* Vi- 

 trunus, in his Chapter on Harbours, especially describes the different 



modes of operation before mentioned, with repeat to rubble, and pozzolano 

 walls, coffer-dams, piling, &c. 



From the above account of the ancient port of Ostia, the following ge- 

 neral conclusions may be drawn : — 



First. Thai theancienis were well acquainted with the general princi- 

 ples of design and construclion of harbours. 



Secondly. That as regards the mouth of Ihe Tiber, they carried Ihe im- 

 provements as far as was practicable, and that having arrived at that point, 

 their only resource was to construct an entirely new port elsewhere, free 

 from Ihe difficulties by which the 'I'lber was surrounded. 



Thirdly. That in flat alluvial and deeply embayed coasts like those ad- 

 jacent to the Tiber, it is a matter of the first consequence to ascertain by 

 practical experience, the extent to which the coast line may be expected 

 to advance, from the construction of works at Ihe mouth of 'a river. This 

 point being first decided, if further iniprovenients be required, then tire 

 question of a new harbour free from Ihe difficulties of the old river port 

 may be entertained ; and its conslruclicm should be so designed as lo give 

 the required prottcliun, without incurring the risk of an injurious accumu- 

 lalion of deposit. The port of Claudius, although it was well desicaed 

 and constructed in ilself, was loo near the mouth of Ihe Tiber to be effec- 

 tual, and in fact it acted like a great jetty or conlinuation of the old woiks 

 at the mouth of the Tiber ; thereby obstructing the free action of Ihe cu»- 

 rent and producing stagnation ou both sides, and by thus, lo a certain ex. 

 teni, facilitating the deposit of alluvial matter, which it was intended \o 

 obviate, it became overwhelmed and destroyed. 



Fourthly. The fate of the port of Claudius and Trajan demonstrated 

 the impracticability of making an effectual harbour near the mouth of the 

 Tiber. Trajan therefore determined lo select an entirely new site free 

 from the difficulties of Ihe old, and, wilh that view, constructed Ihe well 

 known port of Civila Vecchia, anciently called Centum Cellse, which has 

 been preserved lo the present time, a monument of skill and ingenuity in 

 this department of construction. Upon the whole, therefore, the history 

 of the port of Oslia is replete with inslruction, as we at once see exempli- 

 fied nearly all the various departnienls of harbour construction, bolh theo- 

 retical and practical, together with their usual results, and it is only by a 

 careful study of this and similar examples, combined with a correct know- 

 ledge of the various local circumslauces, that we can obtain a complete 

 knowledge of this difficult but highly useful and important branch of Civil 

 Engineeriug. 



THE CASTLE OF OSTIA. 



^|;'3^^S: 



* Qy Is not Caligula's Bridge > sufficient test of time?- Ed. C. E. & A. Journal. 



[From a Sketch by Mr. EiplngiUe in 18J4.] 

 ^ Rfmrn-fo.-After the paper was read, the following observations were 



i*'u ,^j u'"^ \^ listened with much interest to the excellent paper 

 which had been read ; it was full of instructive, practical facts He liad 

 been forcibly struck with the similarity of Ihe results described, to the effects 

 which were daily under the observation of engineers, in the harbours of the 

 south coast of England. Rye, Dover, and Shoreham, might be quoted as 

 examples. Of the ancient harbour of Rye, scarcely any traces remained. 

 Mr. Giles was sent to Dover by the late Mr. Rennie, during the last year of 

 the Pitt administration, in 1805, with instructions to make a survey for the 

 purpose of forming an extensive harbour of refuge for the Channel fleet' 

 The design was not proceeded with, but certain improvements were com- 

 menced, n^ith the view of removing tie mass of shingle on the bar, and pre- 

 venting a further accumulation. Mr. Walker had since done much for the 

 further improvement of Ihe harbour, by extruding the backwater, and affoid- 

 mg greater power of scouring by sluices. There was still great room for 

 improveirrent ; and, although there was at present rarely such an accnmula- 

 tion of kiiMgle across the enlisnce, altir a stoim, as to close it up, which 

 frequently occurred in former times : jet it was evident, that where'er piers 

 or other obstacles were projected directly from the shore, the shingle would 

 accumulate against them, and turning the point, would be thrown, in the 

 form of a bar, across the entrance. This had become to evident, that the 



